Complete NI-ZN Battery Information

Pub. No.: Publication Date:

WO/2008/036948 27.03.2008

International Application No.: International Filing Date:

PCT/US2007/079237 21.09.2007

IPC:

H02J 7/16 (2006.01), H02J 7/00 (2006.01)

Applicants:

POWERGENIX SYSTEMS, INC. [US/US]; 10109 Carroll Canyon Road, San Diego, California 92131-1109 (US) (All Except US).

ALGER, Ethan [US/US]; (US) (US Only).

PHILLIPS, Jeffrey [GB/US]; (US) (US Only).

BENDERT, Richard [US/US]; (US) (US Only).

MOHANTA, Samaresh [CA/US]; (US) (US Only).

Inventors:

ALGER, Ethan; (US).

PHILLIPS, Jeffrey; (US).

BENDERT, Richard; (US).

MOHANTA, Samaresh; (US).

Agent:

SHU, Cindy, H. et al.; Beyer Weaver LLP, P. O. Box 70250, Oakland, California 94612-0250 (US) .

Priority Data: 60/846,518 21.09.2006 US Title:

CHARGING METHODS FOR NICKEL-ZINC BATTERY PACKS

Abstract:

A temperature-compensated constant voltage battery charging algorithm charges batteries quickly and safely.

Charging algorithms also include methods to recondition batteries after storage and to correct cell imbalances in a battery pack. A battery charger able to perform these functions is also disclosed.

Designated States:

AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ, CA, CH, CN, CO, CR, CU, CZ, DE, DK, DM, DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, HN, HR, HU, ID, IL, IN, IS, JP, KE, KG, KM, KN, KP, KR, KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD, ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ, OM, PG, PH, PL, PT, RO, RS, RU, SC, SD, SE, SG, SK, SL, SM, SV, SY, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW. African Regional Intellectual Property Org. (ARIPO) (BW, GH, GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM, ZW) Eurasian Patent Organization (EAPO) (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM) European Patent Office (EPO) (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HU, IE, IS, IT, LT, LU, LV, MC, MT, NL, PL, PT, RO, SE, SI, SK, TR) African Intellectual Property Organization (OAPI) (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG).

Publication Language:

English (EN)

Filing Language:

English (EN)

PowerGenix Nickel-Zinc Charge Procedure Two Step Charge 1. Constant Current: From 1.0 to 2.0 Amps to 1.9V/Cell 2. Constant Voltage: 1.9V/Cell to Current < 90mA Fault Conditions * Total charge time exceeds 2.5 hrs * Temperature of the cell rises by more than 15C * Voltage is less than 1.6V Notes: For Laboratory Testing: Non temperature compensation at 25°C +/_ 3 degrees Temperature Compensated Charge Procedure Two Step Charge *Temperature Compensated Voltage (TCV) = 1.90 - (0.003 x (T-25ºC) V/Cell * Constant Current 2A to TCV * Constant Voltage TCV to I < 90 mA Fault Conditions Stop Charge if the any of the following conditions occur: * Total charge time exceeds 2.5 hrs * Temperature of the cell rises by more than 15ºC *Temperature of the cell exceeds 40ºC *Voltage is less than 1.6V Charge Characteristics at 25°C Maintenance Charge Procedure Recharge cell/pack per Standard Charge Procedure if: Volts per cell < 1.68 V Time since last full charge > 30 days

WO 2008036948 20080327 CHARGING METHODS FOR NICKEL-ZINC BATTERY PACKS FIELD OF THE INVENTION The present invention relates to the rechargeable battery arts and, more particularly to nickel zinc rechargeable battery cells and packs. Even more specifically, this invention pertains to methods of charging sealed nickel zinc rechargeable battery cells.

BACKGROUND The method of charging a nickel zinc battery is important to its performance. Performance factors such as battery life, specific capacity, charging time, and cost can all be affected by the method of charging. Charger designers must balance the need for a fast charge, therefore a quick return to service, and low cost charger with the other needs such as cell balancing, increasing life, and preserving capacity.

Nickel zinc battery charging poses particular challenges because the nickel electrode charging potential exists at a voltage very close to the oxygen evolution potential. During battery charging, the oxygen evolution process competes with the nickel electrode charging process as a function of the state-of-charge of the nickel electrode, charging current density, geometry, and

temperature.

During the charging of a conventionally designed nickel zinc cell with excess zinc, oxygen evolution occurs before the nickel becomes fully charged. Nickel zinc batteries use membrane separators between the electrodes that limit the transport and oxygen access to the zinc electrode for direct recombination. Therefore, the rate at which oxygen can recombine at the zinc electrode is limited because the oxygen must travel to the ends of the electrode to cross the membrane separator. This challenge is particular to the nickel zinc battery because some other battery types, such as nickel cadmium batteries, do not employ separators having the same resistance to oxygen mobility. Thus, nickel zinc batteries are limited by their relatively lower oxygen recombination rates. In a sealed cell in the oxygen evolution regime, charging current density must not exceed the threshold above which oxygen would be created faster than the recombination within the cell, or oxygen pressure will build up.

Because of the oxygen evolution, the nickel zinc battery may require an "overcharge" to fully replace the nickel electrode's capacity. In other nickel battery types' charging schemes, this overcharge can be performed reasonably quickly. In the case for nickel zinc, however, the lower recombination rate limits the use of overcharging to cure the imbalance. Instead of overcharging at the rate of C/3 for nickel cadmium batteries, nickel zinc batteries can only overcharge at the rate of between C/100 and C/10, typically between 40 and 200 milliamps for 2 Amp-hour cells.

Classic charging schemes include constant potential and constant current. In order to avoid oxygen pressure build up in nickel zinc cells, a constant current scheme could necessitate too low of a current to allow fast charging. In a constant voltage scheme, cell imbalances are exacerbated to reduce the life of battery packs. When the voltage is constant, the weaker cell in series with stronger cells charges at a lower voltage than the stronger cells, further exacerbating its lower level of charge. Other charging schemes include multistage constant current schemes and pulse charge with discharge cycles. The more complex is the charging scheme, the more expensive is the charger.

After storage or shipping at high temperature, some battery packs are found to have high impedance, caused perhaps by a passivation layer on the electrode. These batteries will only charge slowly, because the high impedance allows only a low current at constant voltage. At a high constant current, these batteries quickly reach the voltage limit. In order to fast charge these batteries, the passivation layer must be removed to reduce the impedance.

What are needed, therefore, are charging methods that are fast, low cost, address charging imbalances among cells in a battery pack, charge batteries with high impedance, and are safe for the batteries and consumers.

SUMMARY The present invention provides novel charging schemes to quickly charge a nickel zinc battery pack, cure imbalanced cells in a battery pack, cure high impedance resulting during shipment or storage, and do all this safely and cheaply for the battery and the consumer.

Several charging schemes are presented: a bulk charge algorithm for charging most batteries; a front-end charge algorithm for manual and automatic reconditioning of batteries; an end-ofcharge termination algorithm; a state-of-charge maintenance charge algorithm to ensure that the cell/battery is always charged while attached to a charger; and several alternate charge algorithms. Any of these may be used alone or in combination. A few preferred combinations are set forth herein, but the invention is not limited to these.

In one aspect, the present invention pertains to a method of charging a nickel- zinc battery at a constant current, then at a constant voltage. The method includes measuring a temperature of the battery, calculating a voltage based on at least the temperature of the battery, charging the battery at a constant current (CI) until the calculated voltage is reached, charging the battery at a calculated voltage (CV) per nickel-zinc cell, and stopping the charging at the calculated voltage per cell when an end of charge condition is satisfied. Note that there may be one or more cells in a battery. Typically, the cells are connected in series.

During the CI step, the battery is charged at, e.g., 1-2 Amps until either (a) the voltage is equal to or greater than a threshold voltage (which may be temperature compensated) multiplied by the number of cells being charged in series, (b) a specified time has elapsed (e.g., one hour), or (c) the temperature of the battery rises by a specified amount (e.g., about 15 degrees Celsius or higher). The battery temperature is optionally measured by a thermocouple, thermistor, or other temperature measurement device, typically located in the middle, or the thermal center, of the battery pack. Note that the parameter values listed here and elsewhere in this summary were chosen for a typical nickel zinc battery having a capacity of approximately 2 Amp-hours. Those of skill in the art will appreciate that some parameters values may be scaled with the battery capacity. In some embodiments, linear scaling is appropriate.

After the optional constant current stage of charging is complete, the bulk charging algorithm proceeds to the CV step. Here the battery is charged at the temperature compensated voltage multiplied by the number of cells until an end-of charge condition is satisfied. The end-ofcharge condition may be that the current reduces to less than or equal to a set value (e.g.,

about 90 milliamps per cell), a set time has elapsed (e.g., about 1.5 hours), the current is greater than or equal to a defined threshold value associated with a short circuit in the battery (e.g., about 2.25 Amps for a 2 Amp- hour battery), the temperature rises by a defined amount (e.g., about 15 degrees Celsius or more - e.g., to an temperature of 37 degrees Celsius), or a combination of these.

The temperature compensated voltage is a function of the battery temperature and, in some embodiments, a percentage state-of-charge, electrolyte composition, and the constant stage charge current. Depending on the sophistication of the charging hardware, temperature compensation equations of varying complexity may be used. In one embodiment, the charger employs a quadratic equation, but other embodiments include a linear equation or two linear equations for different temperature ranges, as shown in Table 1. Equations for various states of charge (identified as percentages of complete charge) are provided. Once the temperature compensated voltage is determined, it is used in the bulk charge algorithm (e.g., as the voltage cutoff for the constant current stage of the charge process). The algorithm will update temperature compensated voltage as the battery temperature changes over time during charging. In certain embodiments, the temperature compensated voltage used during the CV phase is about 1.9 to 1.94 volts. In certain embodiments, this voltage is appropriate for use when the cell being charged has a temperature in the range of about 20-25 degrees Celsius, preferably about 22 degrees Celsius. Further, the 1.9 to 1.94 voltage may be appropriate for nickel-zinc batteries having electrolytes with a free unbuffered alkalinity of between about 5 and 8.5 molar. In certain embodiments, an expression used for temperature compensated voltage during the CV phase is _V=0.0044*T+2.035 where V is the constant voltage value and T is the temperature in degrees Centigrade.

In certain embodiments employing nickel zinc cells employing high conductivity electrolytes, e.g., electrolytes having a conductivity in the range of about 0.5 to 0.6 (ohm cm) "1, the constant voltage employed during the CV phase may be reduced by some amount. In one embodiment, the CV set voltage is reduced by about 10 to 20 millivolts compared with the level described above. Thus, in some cases, the set voltage during the CV phase may be about 1.88 to 1.92 volts. Similarly, the transition from CI to CV may occur when the cell voltage reaches about 1.88 to 1.92 volts during the CI phase in charging a nickel zinc cell.

In a particular embodiment, the charging method includes a front-end charge algorithm that checks first for battery temperature to be within a certain range, e.g., between about 0 and 45 degrees Celsius. If the temperature is outside this range, then the algorithm will apply a trickle current or equivalent current pulse between about 100 to 200 milliamps per 2 amp hour of battery capacity until the temperature rises to about 15 degrees Celsius (or other specified temperature), voltage reaches a minimum of, e.g., one volt per cell, or the time limit of, e.g., about 20hr @ C/20 rate is reached without the temperature increase or minimum voltage. If the temperature is within the range, then the front-end charge algorithm is skipped and the constant voltage or constant current/constant voltage charging may start.

In certain embodiments, a front-end algorithm may be activated automatically by the charger logic or manually, e.g., by the user pressing a reconditioning button. If the constant current step of the bulk charge algorithm reaches its voltage endpoint (e.g., 1.9 volts) too quickly, e.g., within 0-10 minutes, preferably within 5 minutes, then the front-end algorithm may start automatically to recondition the battery pack. This algorithm has been found to be helpful for those batteries having a high impedance resulting from, possibly, passivation during storage or shipping. The lower-than-normal current provided in the front-end charge may reform the electrode components and thereby remove a passivation layer (e.g., a passivation layer on the zinc electrode).

An end-of-charge termination algorithm may be added after the end-of-charge condition is satisfied or may be implemented by a charger when a battery pack has greater than about 90% state-of-charge. In one embodiment, the end-of-charge termination algorithm comprises of a first corrective current between about 50 to 200 milliamps per 2 amp hour of battery capacity for about 30 minutes to 2 hours, preferably at about 100 milliamps per 2 amp hour of battery capacity for about 1 hour. There is no voltage limit for this step. This algorithm is found to at least partially overcome cell imbalances in a battery pack. The fixed current forces a certain level of current to pass through each cell equally - thus allowing weaker cells to charge to a level not necessarily attained with constant voltage and thereby reducing differences between strong and weak cells. The algorithm has been found to increase battery life.

The state-of-charge maintenance algorithm can be used to ensure that the cell/battery has, e.g., about 80% or greater state-of-charge while attached to a charger. This algorithm may be a second half of the end-of-charge termination algorithm after the corrective current or may stand alone. One embodiment of this algorithm employs a constant current charge of about 0-50 milliamps per 2 amp hour of battery capacity or equivalent current pulsing. In another embodiment, the battery pack can receive a full charge cycle (standard charge algorithm)

periodically if the voltage of the pack is between, e.g., about 1.71V to 1.80V per cell.

The temperature compensated voltage used in some of the algorithms may be recalculated constantly or periodically. Thus the voltage applied during the constant voltage phase may change as the battery temperature changes. The temperature measuring and calculating operations of the charging method may thus repeat during charging.

Certain alternative charge algorithms may include a multi-stepped constant charge algorithm to defined voltage limits (e.g., temperature compensated voltage limits). In some examples, about ten steps are used. In one example, a constant current is applied initially until the voltage reaches the defined voltage limit. Then the current is stepped down by a defined factor until the voltage again reaches the defined limit. The process may repeat until a defined level of charge is reached. This approach may be employed in cases where very simple chargers are employed, e.g., chargers that are incapable of performing a constant voltage charge. This method of charging a battery includes measuring a temperature and a voltage of the battery, calculating a calculated voltage based on at least the temperature of the battery, charging the battery at a charge current until the battery voltage equals the calculated voltage, reducing the charging current by a defined factor, and charging the battery at the reduced charge current until the battery voltage equals the calculated voltage. The reducing current and charging the battery at the reduced charge operations may be repeated until the current is below a certain amount, signifying that a certain capacity is reached. The defined factor may be about 2-10. This factor may be kept constant in some or all of the steps, or may be varied from step to step. The calculated voltage may be updated continuously by measuring the temperature and recalculating the voltage. In some embodiments, measuring of temperature and voltage occurs periodically, e.g., once every 5 seconds. In some embodiments, these measurements occur independently of each other. Certain other alternate charge algorithms involve using a constant current and terminating the charge based on measured voltage, voltage and time, and/or temperature and time. In the first case the charge is terminated when the voltage level decreases by dV from the maximum, which may be about 0 to 0.020 volts/cell in certain embodiments, preferably about 0 volts/cell. In other words, the charge stops preferably at the inflection point where the voltage stops increasing and is just starting to decrease from the maximum. In a second case, the charge is terminated when the level of voltage decreases relative to time by the amount dV/dt. In other words, the charger will terminate the charge when voltage decreases by a pre-determined amount per cell within a specified time period. Alternatively, the charge may be terminated when the level of voltage does not change over a certain amount of time. Lastly, the charge may be terminated based on the amount of temperature increase relative to time, or dT/dt. In other words, the charger will terminate the charge when the battery temperature increases by a specified amount within a specified time period.

In certain embodiments, a method of charging a nickel-zinc cell may include charging the nickel-zinc battery at a constant current until reaching a point at which (i) the cell's state of charge is at least about 70%, (ii) a nickel electrode of the cell has not yet begun to evolve oxygen at a substantial level, and (iii) the cell voltage is between about 1.88 and 1.93 volts or between about 1.88 and 1.91 volts; and charging the nickel-zinc battery at a constant voltage in the range of 1.88-1.93 until an end-of- charge condition is satisfied. In some cases, the constant current may be most about 4 Amps per 2 Amp hour battery capacity when the "1 nickel-zinc battery employs an electrolyte having a conductivity of at least about 0.5 cm ohm ~ \ In some embodiments, a lower constant current may be used, at about 2 amps or at about 1.5 amps.

Note that in this embodiment, no measurement of cell temperature or calculation is necessary.

Any one or more of the charging methods described herein may be employed on chargers singly or in combination. The logic required may be hardwired into the charger by using various electronic components, be programmed with a low cost programmable logic circuit (PLC), or be custom designed on a chip (e.g., an ASIC). Also the charger may be integrated into a consumer product, such as where the logic is programmed into the power tool or device powered by the battery. In some of these cases, the logic may be implemented in the electric circuitry directly integrated into the consumer product, or be a separate module that may or may not be detachable.

The present invention also pertains to a nickel-zinc battery charger. The charger may include an enclosure for holding the nickel-zinc battery, a thermistor configured to thermally couple to a battery during operation, and a controller configured to execute a set of instructions. The charger may also include a recondition button. The enclosure need not completely surround the battery, e.g., the enclosure may have an open face. The enclosure may also have a door or lid to allow for easy access to the battery. During charging operations, the thermistor may contact an external surface of a cell in the thermal center of a battery pack. The set of instructions may include instructions to measure a temperature of the battery, calculate a calculated voltage, charge the battery at the calculated voltage, and stop the charge at the calculated voltage when an end-of-charge condition is detected. The instructions may also include

instructions to charge the battery at a constant current, charge the battery at a corrective current, or charge the battery at a minimum current. The instructions may also include instructions to charge the battery at an initial current when the recondition button is pressed.

Additionally, the charger may include other interface with which the user may interact with the charger or the charger may communicate with the user, e.g., color lights to indicate completion of charging or that the battery is bad. These and other features and advantages of the invention will be described in more detail below with reference to the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simple schematic of a charger connected to a battery pack in accordance with the present invention.

Figures 2A and 2B are graphs of charge curves at various battery temperatures of constant current charging at 1 Amp and 2 Amps, respectively.

Figure 3 is a graph of charge curves for various electrolyte compositions.

Figure 4 is a graph of a constant current/constant voltage charge algorithm over time in accordance with some embodiments of the present invention.

Figure 5 is a graph of a battery charging algorithm over time in accordance with some embodiments of the present invention.

Figure 6A is an exploded diagram of a nickel zinc battery cell in accordance with the present invention.

Figure 6B is a diagrammatic cross-sectional view of an assembled nickel zinc battery cell in accordance with the present invention.

Figure 7 presents a diagram of a cap and vent mechanism according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Introduction In the following detailed description of the present invention, numerous specific embodiments are set forth in order to provide a thorough understanding of the invention. However, as will be apparent to those skilled in the art, the present invention may be practiced without these specific details or by using alternate elements or processes within the spirit and scope of the invention. In other instances well-known processes, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the present invention.

Although many charging schemes are presented, it should be understood that not all charging methods need to be configured on the same charger. A charger may employ these methods singly or in combination. Further, a charger may or may not allow user interaction to provide manual selection of a charging algorithm or even selection of a parameter within a particular charging algorithm. Particularly, a "recondition" button may be provided which the user may select to start the front-end charge algorithm. For truly low cost chargers, user interaction with the charger may be limited to little if any manual input, relying instead on the logic of the charger.

A battery may include one or more cells. If more than one cell, the cells are electrically connected to each other serially. In this disclosure, the terms battery and "battery pack" are used interchangeably. Unless otherwise noted, parameters specified herein pertains to a 2 Amp hour cell.

Figure 1 shows a simple schematic of a charger 104 connected to a 9-cell battery pack. In the depicted embodiment, a variable alternating current 102 enters the charger 104, which is wired to a positive terminal 108 and a negative terminal 106. The cells are wired in series. A thermocouple or a thermistor 110 is attached to the center of the battery pack and provides temperature inputs to the charger 104.

Bulk Charge Algorithm with Temperature Compensation (CI/CV) A bulk charge algorithm applies to many charging situations. It is fast and cost effective. If unmitigated, oxygen evolution is particularly problematic in nickel- zinc battery cells. The bulk charge algorithm generally includes at least two stages, a constant current (CI) stage where the majority of charging, e.g., up to 80% state-of- charge, takes place and a constant voltage (CV) stage where efficient charging takes place while taking into account the oxygen evolution. The constant voltage (CV) charging at or below a voltage at which the oxygen evolution/recombination reactions may be sustained in balance without undue increase in cell pressure and/or temperature. In certain embodiments, the CI stage is performed in a step-wise manner, which each succeeding step performed at a lower current.

During the CI step, the battery is charged at a constant current (e.g., about 1-2 Amps) until one of various conditions is satisfied. The desired condition is that the charging reaches a defined voltage (e.g., about 1.9 volts/cell) within a reasonable and expected time frame. In particular embodiments, the defined voltages are temperature compensated. This defined voltage may correspond to a state-of-charge at about 70- 80%, or preferably about 80%. In certain embodiments, the defined voltages depend on battery temperature, electrolyte composition (e.g., alkalinity) and the initial constant charge current. After the voltage threshold condition is satisfied, then the battery transitions to charging in the CV step.

The temperature compensated voltage is a function of the battery temperature and a percentage state-of-charge. The complexity of the temperature compensation calculation may be dictated by the level of sophistication of the charger (and consequently its expense). Its value is defined by using, e.g., a quadratic equation, a linear equation, or two linear equations for different temperature ranges (above and below 20 degrees Celsius). Table 1 shows the constant values for each equation for different percentage state-of-charge between 50 and 90 2 percent. The equations are: Quadratic: a (T) + b (T) + c Linear: m (T) + V where T is the measured temperature and a, b, c, m, and V are constants provided in Table 1. For sophisticated chargers, the quadratic equation may be desirable, as it may closely approximate the temperature compensated voltage. However, the linear equations are likely used in implementation when the charger is limited to simpler logic (which is expected to be the situation with inexpensive chargers (e.g., about US$5/charger)).

An important consideration in choosing the appropriate voltage for the termination of the constant current phase of the charge is the time required for charging. It is desirable to charge batteries quickly, so that the battery operated device may return quickly to service. Because charge transfer to the battery is typically higher during the CI step than during the CV step, it is desired that bulk of the charging takes place in the CI step. However, oxygen evolution becomes a concern after continued charging in the CI regime. For single cells this value may be chosen at a voltage corresponding to the measured charge voltage at a given current at approximately 70 - 80% state of charge, depending on factors such as battery temperature and constant charging current. For multicell batteries the voltage value chosen may correspond to a lower state of charge, i.e., 50 to 70% depending on the initial Amp hour capacity distribution spread and how that spread may change over the cycle life of the battery. The state-of-charge at which the CI step is terminated may be limited to a point at which the onset of oxygen evolution occurs during the constant current charge curve taking into account the capacity distribution in a battery pack. Appropriate values of the voltage and their temperature dependence are illustrated in Table 1.

Figure 2A is a graph of charge curves at various battery temperatures of constant current charging at 1 Amp. The graph shows battery voltage versus amp hours charged for 1.8 amp hour nickel zinc cells at temperatures of 0 to 40 degrees Centigrade. Curve 202 corresponds to the charge curve at 0 degrees Centigrade. The voltage increased quickly after very little charging and increases from about 1.87 volts to about 2.075 volts at 1.8 amp hours, corresponding to 100% state-of-charge (SOC) for these cells. Curve 204 corresponds to the charge curve for a battery temperature of 10 degrees Centigrade; curve 206, 20 degrees; curve 208, 30 degrees; and, curve 210 at 40 degrees Centigrade. As the battery temperature increased, a lower voltages correspond to the same charge capacity. For example, at about 1 amp hour, corresponding to 56% SOC for a 1.8 amp hour battery, the battery voltage is about 0 1.845 volts for the 40 C battery. As the battery temperature decreases the voltage became higher and higher at the same SOC. Note that the curves have an "s" shape or upward trend (increasing slope) after a relatively flat plateau. This upward trend generally occurs at relatively higher charged capacities. Though not intended to be bound by this theory, it is believed that the onset of the upward trend indicates the beginning of undesirable oxygen evolution rate.

Generally, battery pressure does not significantly increase and cause a safety concern until the charged capacity is over 100%. However, even some oxygen evolution in excess of the recombination rate may affect the longevity of internal parts and render the charging less effective because not all electrical energy is converted and stored as electrochemical energy.

Thus, the battery voltage is desirably kept below this onset voltage during the entire bulk charging process by switching to a CV step after the CI step reaches this voltage. The temperature compensated voltage may also depend on the electrolyte composition and the constant charging current. Generally, a lower constant charging current reduces the defined voltage at which the charging transitions to the CV regime. Figure 2B is a graph of charge curves at various battery temperatures of constant current charging at 2 Amp. As with the experiments of Figure 2A, these experiments were conducted with nickel zinc cells having a capacity of 1.8 amp hours. Charging curve 212 corresponds to a battery charged at 0 degrees Centigrade; curve 214, 20 degrees; curve 216, 30 degrees, and, curve 218, 40 degrees Centigrade. Compared to Figure 2A, the voltages are generally higher, about up to 30 millivolts or even up to 50 millivolts higher. Note that the point where voltage starts to increase at a higher rate occurs at a lower charged capacity. Thus, the SOC at the transition between CI and CV may be lower if the constant current is higher (e.g., 2 amps versus 1 amp). Although charging at a higher current generally means that the charge is quicker, this may not always be the case. High current CI charging may actually result in a longer total charge time if the CI stage must be terminated at a relatively low SOC due to oxygen evolution considerations. In such cases, the charge must transition to the relatively slower CV stage earlier in the overall charge procedure. A specific example may illustrate the point. At a constant current of 2A, a battery may initiate the CV step at about 60% capacity, which occurs after 40 minutes of charging. However, the remaining 40% capacity with the CV step can take over an hour. At

constant current of IA, a battery may initiate the CV step at about 80% capacity after charging for about 1.5 hours. The remaining 20% capacity may take half hour more. The difference in total charging time between a constant current of IA and 2A may be about half an hour. An optimal constant current for the CI step may be between 1 and 2 amps for this 1.8 amp hour cell, or about 1.5 amps. The difference between the temperature compensated voltage of constant currents at 2 amp and 1 amp may be up to about 30 millivolts or up to about 50 millivolts. The difference between the temperature compensated voltage of constant currents at 2 amp and 0.133 amp may be up to about 80 millivolts.

Table 1 : Example Temperature Compensation Constants Increased electrolyte conductivity may reduce the defined voltage for transition from the CI to the CV charge stage. Figure 3 is a graph of charge curves for various electrolyte compositions.

The electrolyte may be characterized by its conductivity and alkalinity. The composition of the electrolytes in Figure 3 are summarized in Table 2. Compositions A and E have the highest alkalinity, followed by compositions B, C, and D. Compositions A-D have similar conductivity, but composition E is lower. The charge curve for composition E is 301; for composition A is 303; for B, 305; for C, 307; and, for D is 309. Figure 3 shows that the charge curve 401 for composition E reaches the highest voltages earliest during the constant current charging at 2 amps. Thus, in some embodiments the voltage during the CV stage may be decreased in cells employing electrolytes having relatively higher conductivity. Comparing the charge curves of compositions A to E suggests to the inventors that nickel zinc cells having an electrolyte conductivity of about 0.5 to 0.6 (ohm cm) "1 may proceed to a the CV phase at a lower cell voltage, e.g., about 10-20 millivolts lower than would be otherwise appropriate for a nickel zinc cell employing electrolyte having a lower conductivity, e.g., one in the range of about 0.35 to 0.45 (ohm cm) "1. In some but not all cases, constant voltage during the CV stage may also be conducted at a lower set voltage (e.g., in the range of about 1.88 to 1.91 volts). In general, the conductivity of an electrolyte is a complex function of the electrolyte components. Some components of the electrolytes in Figure 3 are presented in Table 2. Alkalinity is one, but far from the only, driving factor in electrolyte conductivity.

Table 2: Electrolyte Compositions Tested in Figure 3 In summary the voltage values are dependent upon at least the conductivity of the electrolyte, the charging current, the number of cells in the battery and the battery temperature. In one embodiment, constant currents for a fast charge are between IA and 2A for a 2 Ah battery.

In operation, the temperature compensated voltage may be continuously calculated from the updated temperature measurement of the battery pack. One preferred way to measure temperature is from a thermocouple or thermistor located in the thermal center of the battery pack, but other methods may be used. Depending on charger design, temperature measurement may be taken intermittently, as in once every minute or a few seconds, or continuously if the logic circuit would permit. To manage the oxygen evolution during battery charging operations at constant voltage, temperature-compensated voltage for about 70-80% state-of-charge may be used.

Figure 4 is graph of a constant current/constant voltage charge algorithm over time in accordance with one embodiment of the present invention. Current is shown on the left y-axis; voltage is shown on the right y-axis. Curve 402 shows the current through the battery pack (6 cells, each having a capacity of approximately 2 Amphours) over time. At time 0, the current starts at 2 amps and stays constant until voltage 404 reaches about 1.9 volts, at about 2200 seconds for the cell tested. The initial voltage gain is very steep, and then the rate of voltage gain starts to decrease at about 200 seconds. The voltage increases almost constantly in this regime, and is then followed by another rate increase. This period, from about 200 second to 2100 seconds (in the graph), is the regime of most efficient charging. The charging battery pack gains most of its stored capacity during this period. As the curve slope increases again, it reaches a shoulder right around the temperature compensated voltage. This shoulder signals the beginning of oxygen evolution. The second condition that may signal the end of the constant current step is a defined elapsed time (e.g., the constant current phase ends after one hour has elapsed). It is anticipated that most battery packs will reach the temperature compensated voltage within one hour. If after one hour the voltage is still less than the temperature compensated voltage, one of various problems may have occurred: the battery may have developed an internal short circuit, the charger measurements may be faulty, or some other battery internal problems may have developed. In that case the algorithm will not go to the CV step. User intervention may be required.

A third condition that may signal the end of the constant current step is if the battery temperature rises by at least a particular defined amount - e.g., about 15 degrees Celsius or more. Just like the second condition, the excessive temperature rise signals something may be wrong with the battery pack. Even though nickel zinc batteries are less prone to thermal runaways that may plague other battery types, excessive thermal energy may mean that oxygen pressure is building up or higher than normal rates of recombination is occurring. It may

also mean that the cell has developed a short. When excessive temperature rise has been detected, the charging algorithm will stop the charging until the user intervenes. The charge can be restarted once the temperature is within acceptable bounds. If the problem repeats then the battery should be disposed of.

The second step in the CI7CV bulk charge algorithm is the constant voltage step. During this step, the battery continues charging at the defined voltage (e.g., a temperature compensated voltage) until one of several conditions is satisfied. The first condition is where the current reduces to below a defined level (e.g., 90 milliamps for a 2 Amp-hour cell). This low current signals that the charging is complete because very little electrical energy is now being converted into chemical energy. The charge is stopped at this point because the battery is almost fully charged, denoted as state of charge (SOC) at 100%. In other embodiments, different current levels may be used as the stop point in order to target different percentages of SOC. After this condition is satisfied, the charging algorithm would end normally.

As seen in Figure 2, the battery cell is held at around 1.9 volts during this step, from about 2200 to 5000 seconds, as shown on curve 204. The current 202 drops steadily initially and levels out slowly. As noted above, during this step oxygen evolution would start. The rate of charge has to be at such a level that oxygen pressure does not build up significantly.

The second condition that may signal the end of the constant voltage step is when 1.5 hours has elapsed. It is anticipated that battery packs employing 2 Amp- hour cells will reach 90 milliamps within about 1.5 hours. However, if after 1.5 hours the current is still higher than 90 milliamps, the charge is terminated normally. This is not a safety limit just an alternate limit.

Just as in the CI step, various safeguard conditions may be built in to ensure the battery is not overcharged or defective. A third condition that may signal the end of the constant voltage step is if the battery temperature rises by a defined amount such as 15 degrees Celsius or more relative to a start time. The start time may be the beginning of battery charging or the beginning of any of the algorithmic steps.

Possible problems are the same as the discussion in the CI step. The last condition is if the current increased to an unexpectedly high value of, e.g., 2.25 amps or more. This high current might signal an internal short circuit.

Understand that many of the specific parameter values recited here (e.g., maximum current, time cutoffs, and temperature compensated voltage constants) are for nickel zinc cells of a particular capacity. Specifically, the recited values are directed to nickel zinc cells having approximately a 2 Amp-hour capacity configured in series in a 6-cell battery pack. Some of the values will have be scaled for cells and battery packs of different capacities, as will be understood by those of skill in the art.

Front-End Charge Algorithm Various "front-end" charge algorithms may be employed prior to bulk charging. One class of such algorithms provides diagnostic tests designed to make sure that the battery can be successfully charged using the standard charge algorithm. The front-end algorithm may be implemented before every charge, automatically, or by user initiation.

In one embodiment, a front-end charge algorithm checks first for battery temperature within an acceptable range for bulk charging (e.g., between about 0 and 45 degrees Celsius). Bulk charging will not be initiated if the temperature is outside this range. In such cases, the algorithm will apply a "trickle" current or equivalent current pulse between about 50 to 200 milliamps per 2 Amp-hour capacity until the temperature rises to an acceptable level for bulk charging (e.g., about 15 degrees Celsius), and/or the cell voltage reaches a minimum of 1 volt per cell, and/or a specified time limit is reached (e.g., about 20 hours have elapsed). When the minimum voltage and/or the temperature is reached, the bulk charge algorithm may start.

In certain embodiments, this algorithm has the voltage and temperature conditions in the disjunctive. For example, it will be satisfied if either the battery is at least 15 degrees Celsius or even the voltage is at least lvolt. Under normal operating conditions, both of these will be satisfied. The algorithm is likely used only when the battery is initially charged, after long-term storage, or the battery is suspected of being damaged. If neither condition is satisfied before the time limit occurs, the standard charge algorithm should not begin. If the voltage is below the limit the battery needs to be replaced. If the battery is below the temperature limit, the charge may be reset.

This algorithm may also be triggered when the voltage reaches the temperature compensated voltage cut off of the CI step in the standard charge algorithm too fast. A 2 Amp-hour battery charged at 2 Amps would normally reach its temperature compensated voltage in between 30 to 60 minutes, but if a passivation layer causes high impedance in the battery, then the time may be reduced to between 0 and 20 minutes. Alternatively, this front-end algorithm may be activated by the user pressing a button to recondition the battery (or otherwise manually initiating). This algorithm has been found to be helpful for those batteries having a passivation buildup. The lower-than-normal current reforms the electrochemical components and thereby removes the passivation layer.

End-of-Charge Termination Algorithm

An end-of-charge termination algorithm may be added to the end of the standard charge algorithm. In one embodiment, the end-of-charge termination algorithm comprises applying a corrective current between about 50 to 200 milliamps for about 30 minutes to 2 hours, preferably at about 100 milliamps for about 1 hour (again assuming a nominally 2 Amp-hour cell). These currents may be scaled for cells having a different capacity. This additional operation is initiated after the constant voltage portion of the charging algorithm is completed.

In a typical application, there is no voltage limit for this step.

In another embodiment, the end-of-charge termination algorithm comprises more than one constant current step. The first step may apply a constant current between about 50 to 200 milliamps for about 30 minutes to 2 hours, preferably at about 100 milliamps for about 1 hour; and the second step would comprise of constant current between about 0 and 50 milliamps for as long as the battery remains on the charger.

Figure 5 shows the addition of an end-of-charge algorithm to the bulk charging algorithm. After the constant voltage CV step, current is held constant in the last CI regime, in the graph after 5000 seconds. Current 502 is held constant at about 100 milliamps, and voltage 504 slowly increases to a little over 2 volts. This algorithm is found to at least partially overcome cell imbalances in a battery pack. The fixed current forces a certain level of current to pass through each cell equally - thus allowing weaker cells to charge to a level not necessarily attained with constant voltage and thereby reducing differences between strong and weak cells. The algorithm is found to increase battery life.

State-of- Charge Maintenance Algorithm The state-of-charge maintenance algorithm can be used to ensure that the cell/battery has, e.g., 80% or greater state-of-charge while attached to a charger. This way, a user can inadvertently leave the charger plugged in for days, weeks, or months and when she retrieves a battery from the charger it will be nearly fully charged and ready for use. One embodiment of this algorithm is to use a constant current charge of between about 0 to 50 milliamps or equivalent current pulsing. This constant current charge would be applied without a voltage limit for as long as the battery remains in the charger. In another embodiment, the battery pack can receive a full charge cycle (bulk charge algorithm) periodically if the voltage of the pack falls to a particular level; e.g., between about 1.71 and 1.80 volts per cell.

Alternate Charge Algorithms Certain alternative charge algorithms may include a multi-stepped constant charge algorithm to defined voltage limits (e.g., temperature compensated voltage limits or temperature and current compensated voltage limits). In some examples, about ten steps are used. First a constant current is applied until the voltage reaches the defined voltage limit. Then the current is stepped down and held constant until the voltage again reaches the defined limit. The process may repeat until a defined level of charge is reached. This approach may be employed in cases where very simple chargers are employed, e.g., chargers that are incapable of performing a constant voltage charge. In one embodiment, each time the current is stepped down, it is stepped by a factor of about 10. Other alternate charge algorithms involve charging at a constant current and then terminating the charge based on measured voltage, voltage and time, and/or temperature and time. In the first case the charge is terminated when the level of voltage decreases by dV from the maximum, which may be about 0 to 0.020 volts/cell in certain embodiments, preferably about 0 volts/cell. In the second case, the charge is terminated when the level of voltage decreases relative to time by the amount dV/dt. In other words, the charger will terminate the charge when voltage decreases by a pre-determined amount per cell within a specified time period. Alternatively, the charge may be terminated when the level of voltage does not change over a certain amount of time. Lastly, the charge may be terminated based on the amount of temperature increase relative to time, or dT/dt. In other words, the charger will terminate the charge when the battery temperature increases by a specified amount within a specified time period.

The Battery Charger A battery charger may use these algorithms singly or in combination. The logic required may be hardwired into the charger by using various electronic components, be programmed with a low cost programmable logic circuit (PLC), or be custom designed on a chip (e.g., an ASIC). One skilled in the art would be able to select the most economical way to deploy the required logic.

The charger may be directly integrated into the consumer product, as the logic may be programmed into the power tool or device powered by the battery. In some of those cases, the logic may be implemented in the electric circuitry within the consumer product, or be a separate module that may or may not be detachable.

The nickel-zinc charger may include an enclosure for holding the nickel-zinc battery, a thermistor configured to thermally couple to a battery during operation, and a controller configured to execute a set of instructions. The charger may also include a recondition button and/or other interface. The enclosure need not completely surround the battery, e.g., the enclosure may have an open face. The enclosure may also have a door or lid to allow f or easy access to the battery and otherwise keep out dust. Depending on the size and shape of the battery, many designs exist for the enclosure of a stand alone battery charger.

During charging operations, the thermistor may contact an external surface of a cell in the thermal center of a battery pack. The thermistor may be rigidly or flexibly attached to the enclosure. In some cases, the thermistor may be inserted manually or automatically af ter the battery has correctly seated in the enclosure.

The set of instructions may include instructions to measure a temperature of the battery, calculate a calculated voltage, charge the battery at the calculated voltage, and stop the charge at the calculated voltage when an end-of-charge condition is detected. The instructions may also include instructions to charge the battery at a constant current, charge the battery at a corrective current, or charge the battery at a minimum current. The instructions may also include instructions to charge the battery at an initial current when the recondition button is pressed. Additionally, the charger may include other interface with which the user may interact with the charger or the charger may communicate with the user, e.g., color lights to indicate completion of charging or that the battery is bad.

General Cell Structure Figures 6A and 6B are graphical representations of the main components of a cylindrical power cell according to an embodiment of the invention, with Figure 6A showing an exploded view of the cell. Alternating electrode and electrolyte layers are provided in a cylindrical assembly 601 (also called a "jellyroll"). The cylindrical assembly or jellyroll 601 is positioned inside a can 613 or other containment vessel. A negative collector disk 603 and a positive collector disk 605 are attached to opposite ends of cylindrical assembly 601. The negative and positive collector disks function as internal terminals, with the negative collector disk electrically connected to the negative electrode and the positive collector disk electrically connected to the positive electrode. A cap 609 and the can 613 serve as external terminals. In the depicted embodiment, negative collector disk 603 includes a tab 607 for connecting the negative collector disk 603 to cap 609. Positive collector disk 605 is welded or otherwise electrically connected to can 613. In other embodiments, the negative collector disk connects to the can and the positive collector disk connects to the cap.

The negative and positive collector disks 603 and 605 are shown with perforations, which may be employed to facilitate bonding to the jellyroll and/or passage of electrolyte from one portion of a cell to another. In other embodiments, the disks may employ slots (radial or peripheral), grooves, or other structures to facilitate bonding and/or electrolyte distribution.

A flexible gasket 611 rests on a circumferential bead 615 provided along the perimeter in the upper portion of can 613, proximate to the cap 609. The gasket 611 serves to electrically isolate cap 609 from can 613. In certain embodiments, the bead 615 on which gasket 611 rests is coated with a polymer coating. The gasket may be any material that electrically isolates the cap from the can. Preferably the material does not appreciably distort at high temperatures; one such material is nylon. In other embodiments, it may be desirable to use a relatively hydrophobic material to reduce the driving force that causes the alkaline electrolyte to creep and ultimately leak from the cell at seams or other available egress points. An example of a less wettable material is polypropylene.

After the can or other containment vessel is filled with electrolyte, the vessel is sealed to isolate the electrodes and electrolyte from the environment as shown in Figure 6B. The gasket is typically sealed by a crimping process. In certain embodiments, a sealing agent is used to prevent leakage. Examples of suitable sealing agents include bituminous sealing agents, tar and VERSAMID速 available from Cognis of Cincinnati, OH. In certain embodiments, the cell is configured to operate in an electrolyte "starved" condition.

Further, in certain embodiments, the nickel-zinc cells of this invention employ a starved electrolyte format. Such cells have relatively low quantities electrolyte in relation to the amount of active electrode material. They can be easily distinguished from flooded cells, which have free liquid electrolyte in interior regions of the cell. As discussed in US Patent Application No. 11/116,113, filed April 26, 2005, titled "Nickel Zinc Battery Design," hereby incorporated by reference, it may be desirable to operate a cell at starved conditions for a variety of reasons. A starved cell is generally understood to be one in which the total void volume within the cell electrode stack is not fully occupied by electrolyte. In a typical example, the void volume of a starved cell after electrolyte fill may be at least about 10% of the total void volume before fill.

The battery cells of this invention can have any of a number of different shapes and sizes. For example, cylindrical cells of this invention may have the diameter and length of conventional AAA cells, AA cells, A cells, C cells, etc.

Custom cell designs are appropriate in some applications. In a specific embodiment, the cell size is a sub-C cell size of diameter 22 mm and length 43 mm. Note that the present invention also may be employed in relatively small prismatic cell formats, as well as various larger format cells employed for various non-portable applications.

Often the profile of a battery pack for, e.g., a power tool or lawn tool will dictate the size and shape of the battery cells. This invention also pertains to battery packs including one or more nickel zinc battery cells of this invention and appropriate casing, contacts, and conductive lines to permit charge and discharge in an electric device.

Note that the embodiment shown in Figures 6A and 6B has a polarity reverse of that in a conventional NiCd cell, in that the cap is negative and the can is positive. In conventional power cells, the polarity of the cell is such that the cap is positive and the can or vessel is negative.

That is, the positive electrode of the cell assembly is electrically connected with the cap and the negative electrode of the cell assembly is electrically connected with the can that retains the cell assembly. In a certain embodiments of this invention, including that depicted in Figures 6 A and 6B, the polarity of the cell is opposite of that of a conventional cell. Thus, the negative electrode is electrically connected with the cap and the positive electrode is electrically connected to the can. It should be understood that in certain embodiments of this invention, the polarity remains the same as in conventional designs - with a positive cap.

The can is the vessel serving as the outer housing or casing of the final cell. In conventional nickel-cadmium cells, where the can is the negative terminal, it is typically nickel-plated steel.

As indicated, in this invention the can may be either the negative or positive terminal. In embodiments in which the can is negative, the can material may be of a composition similar to that employed in a conventional nickel cadmium battery, such as steel, as long as the material is coated with another material compatible with the potential of the zinc electrode. For example, a negative can may be coated with a material such as copper to prevent corrosion. In embodiments where the can is positive and the cap negative, the can may be a composition similar to that used in convention nickel-cadmium cells, typically nickel-plated steel.

In some embodiments, the interior of the can may be coated with a material to aid hydrogen recombination. Any material that catalyzes hydrogen recombination may be used. An example of such a material is silver oxide. Venting Cap Although the cell is generally sealed from the environment, the cell may be permitted to vent gases from the battery that are generated during charge and discharge. A typical nickel cadmium cell vents gas at pressures of approximately 200 Pounds per Square Inch (PSI). In some embodiments, a nickel zinc cell of this invention is designed to operate at this pressure and even higher (e.g., up to about 300 PSI) without the need to vent. This may encourage recombination of any oxygen and hydrogen generated within the cell. In certain embodiments, the cell is constructed to maintain an internal pressure of up to about 450 PSI and or even up to about 600 PSI. In other embodiments, a nickel zinc cell is designed to vent gas at relatively lower pressures. This may be appropriate when the design encourages controlled release of hydrogen and/or oxygen gases without their recombination within the cell.

Figure 7 is a representation of a cap 701 and vent mechanism according to one embodiment of the invention. The vent mechanism is preferably designed to allow gas but not electrolyte to escape. Cap 701 includes a disk 708 that rests on the gasket, a vent 703 and an upper portion 705 of cap 701. Disk 708 includes a hole 707 that permits gas to escape. Vent 703 covers hole 707 and is displaced by escaping gas. Vent 703 is typically rubber, though it may be made of any material that permits gas to escape and withstands high temperatures. A square vent has been found to work well. Upper portion 705 is welded to disk 708 at weld spots 709 and includes holes 711 to allow the gas to escape. The locations of weld spots 709 and 711 shown are purely illustrative and these may be at any suitable location. In a preferred embodiment, the vent mechanism includes a vent cover 713 made of a hydrophobic gas permeable membrane. Examples of vent cover materials include microporous polypropylene, microporous polyethylene, microporous PTFE, microporous FEP, microporous fluoropolymers, and mixtures and co-polymers thereof (see e.g., US Patent No. 6,949,310 (J. Phillips), "Leak Proof Pressure Relief Valve for Secondary Batteries," issued September 27, 2005, which is incorporated herein by reference for all purposes). The material should be able to withstand high temperatures. In certain embodiments, hydrophobic gas permeable membranes are used in conjunction with a tortuous gas escape route. Other battery venting mechanisms are known in the art and are suitable for use with this invention. In certain embodiments, a cell's materials of construction are chosen to provide regions of hydrogen egress. For example, the cells cap or gasket may be made from a hydrogen permeable polymeric material. In one specific example, the outer annular region of the cell's cap is made from a hydrogen permeable material such as an acrylic plastic or one or more of the polymers listed above. In such embodiments, only the actual terminal (provided in the center of the cap and surrounded by the hydrogen permeable material) need be electrically conductive. The Negative Electrode Generally the negative electrode includes one or more electroactive sources of zinc or zincate ions optionally in combination with one or more additional materials such as conductivity enhancing materials, corrosion inhibitors, wetting agents, etc. as described below. When the electrode is fabricated it will be characterized by certain physical, chemical, and morphological features such as coulombic capacity, chemical composition of the active zinc, porosity, tortuosity, etc.

In certain embodiments, the electrochemically active zinc source may comprise one or more of the following components: zinc oxide, calcium zincate, zinc metal, and various zinc alloys. Any of these materials may be provided during fabrication and/or be created during normal cell

cycling. As a particular example, consider calcium zincate, which may be produced from a paste or slurry containing, e.g., calcium oxide and zinc oxide.

If a zinc alloy is employed, it may in certain embodiments include bismuth and/or indium. In certain embodiments, it may include up to about 20 parts per million lead. A commercially available source of zinc alloy meeting this composition requirement is PGlOl provided by Noranda Corporation of Canada.

The zinc active material may exist in the form of a powder, a granular composition, etc.

Preferably, each of the components employed in a zinc electrode paste formulation has a relatively small particle size. This is to reduce the likelihood that a particle may penetrate or otherwise damage the separator between the positive and negative electrodes.

Considering electrochemically active zinc components in particular (and other particulate electrode components as well), such components preferably have a particle size that is no greater than about 40 or 50 micrometers. In certain embodiments, the material may be characterized as having no more than about 1% of its particles with a principal dimension (e.g., diameter or major axis) of greater than about 50 micrometers. Such compositions can be produced by, for example, sieving or otherwise treating the zinc particles to remove larger particles. Note that the particle size regimes recited here apply to zinc oxides and zinc alloys as well as zinc metal powders.

In addition to the electrochemically active zinc component(s), the negative electrode may include one or more additional materials that facilitate or otherwise impact certain processes within the electrode such as ion transport, electron transport (e.g., enhance conductivity), wetting, porosity, structural integrity (e.g., binding), gassing, active material solubility, barrier properties (e.g., reducing the amount of zinc leaving the electrode), corrosion inhibition etc.

For example, in some embodiments, the negative electrode includes an oxide such as bismuth oxide, indium oxide, and/or aluminum oxide. Bismuth oxide and indium oxide may interact with zinc and reduce gassing at the electrode. Bismuth oxide may be provided in a concentration of between about 1 and 10% by weight of a dry negative electrode formulation.

It may facilitate recombination of hydrogen and oxygen. Indium oxide may be present in a concentration of between about 0.05 and 1% by weight of a dry negative electrode formulation.

Aluminum oxide may be provided in a concentration of between about 1 and 5% by weight of a dry negative electrode formulation.

In certain embodiments, one or more additives may be included to improve corrosion resistance of the zinc electroactive material and thereby facilitate long shelf life. The shelf life can be critical to the commercial success or failure of a battery cell. Recognizing that batteries are intrinsically chemically unstable devices, steps should be taken to preserve battery components, including the negative electrode, in their chemically useful form. When electrode materials corrode or otherwise degrade to a significant extent over weeks or months without use, their value becomes limited by short shelf life. Specific examples of anions that may be included to reduce the solubility of zinc in the electrolyte include phosphate, fluoride, borate, zincate, silicate, stearate, etc. Generally, these anions may be present in a negative electrode in concentrations of up to about 5% by weight of a dry negative electrode formulation. It is believed that at least certain of these anions go into solution during cell cycling and there they reduce the solubility of zinc. Examples of electrode formulations including these materials are included in the following patents and patent applications, each of which is incorporated herein by reference for all purposes: U.S. Patent No. 6,797,433, issued September 28, 2004, titled, "Negative Electrode Formulation for a Low Toxicity Zinc Electrode Having Additives with Redox Potentials Negative to Zinc Potential," by Jeffrey Phillips; U.S. Patent No. 6,835,499, issued December 28, 2004, titled, "Negative Electrode Formulation for a Low Toxicity Zinc Electrode Having Additives with Redox Potentials Positive to Zinc Potential," by Jeffrey Phillips; U.S. Patent No. 6,818,350, issued November 16, 2004, titled, "Alkaline Cells Having Low Toxicity Rechargeable Zinc Electrodes," by Jeffrey Phillips; and PCT/NZ02/00036 (publication no. WO 02/075830) filed March 15, 2002 by Hall et al.

Examples of materials that may be added to the negative electrode to improve wetting include titanium oxides, alumina, silica, alumina and silica together, etc. Generally, these materials are provided in concentrations of up to about 10% by weight of a dry negative electrode formulation. A further discussion of such materials may be found in U.S. Patent No. 6,811,926, issued November 2, 2004, titled, "Formulation of Zinc Negative Electrode for Rechargeable Cells Having an Alkaline Electrolyte," by Jeffrey Phillips, which is incorporated herein by reference for all purposes.

Examples of materials that may be added to the negative electrode to improve electronic conductance include various electrode compatible materials having high intrinsic electronic conductivity. Examples include titanium oxides, etc. Generally, these materials are provided in concentrations of up to about 10% by weight of a dry negative electrode formulation. The exact concentration will depend, of course, on the properties of chosen additive. Various organic materials may be added to the negative electrode for the

purpose of binding, dispersion, and/or as surrogates for separators. Examples include hydroxylethyl cellulose (HEC), carboxymethyl cellulose (CMC), the free acid form of carboxymethyl cellulose (HCMC), polytetrafluoroethylene (PTFE), polystyrene sulfonate (PSS), polyvinyl alcohol (PVA), nopcosperse dispersants (available from San Nopco Ltd. of Kyoto Japan), etc.

In a specific example, PSS and PVA are used to coat the negative electrode to provide wetting or other separator-like properties. In certain embodiments, when using a separator-like coating for the electrode, the zinc-nickel cell may employ a single layer separator and in some embodiments, no independent separator at all. In certain embodiments, polymeric materials such as PSS and PVA may be mixed with the paste formation (as opposed to coating) for the purpose of burying sharp or large particles in the electrode that might otherwise pose a danger to the separator.

When defining an electrode composition herein, it is generally understood as being applicable to the composition as produced at the time of fabrication (e.g., the composition of a paste, slurry, or dry fabrication formulation), as well as compositions that might result during or after formation cycling or during or after one or more charge-discharge cycles while the cell is in use such as while powering a portable tool. Various negative electrode compositions within the scope of this invention are described in the following documents, each of which is incorporated herein by reference: PCT Publication No. WO 02/39517 (J. Phillips), PCT Publication No. WO 02/039520 (J. Phillips), PCT Publication No. WO 02/39521, PCT Publication No. WO 02/039534 and (J. Phillips), US Patent Publication No. 2002182501. Negative electrode additives in the above references include, for example, silica and fluorides of various alkaline earth metals, transition metals, heavy metals, and noble metals.

Finally, it should be noted that while a number of materials may be added to the negative electrode to impart particular properties, some of those materials or properties may be introduced via battery components other than the negative electrode. For example, certain materials for reducing the solubility of zinc in the electrolyte may be provided in the electrolyte or separator (with or without also being provided to the negative electrode). Examples of such materials include phosphate, fluoride, borate, zincate, silicate, stearate. Other electrode additives identified above that might be provided in the electrolyte and/or separator include surfactants, ions of indium, bismuth, lead, tin, calcium, etc.

US Patent Application No. 10/921,062 (J. Phillips), filed August 17, 2004, hereby incorporated by reference, describes a method of manufacturing a zinc negative electrode of the type that may be employed in the present invention.

Negative Electronic Conduction Pathway The negative electronic pathway is comprised of the battery components that carry electrons between the negative electrode and the negative terminal during charge and discharge. One of these components is a carrier or current collection substrate on which the negative electrode is formed and supported. This is a subject of the present invention. In a cylindrical cell design, the substrate is typically provided within a spirally wound sandwich structure that includes the negative electrode material, a cell separator and the positive electrode components (including the electrode itself and a positive current collection substrate). As indicated, this structure is often referred to as a jellyroll. Other components of the negative electronic pathway are depicted in Figure IA. Typically, though not necessarily, these include a current collector disk (often provided with a conductive tab) and a negative cell terminal. In the depicted embodiment, the disk is directly connected to the negative current collector substrate and the cell terminal is directly attached to the current collector disk (often via the conductive tab). In a cylindrical cell design, the negative cell terminal is usually either a cap or a can.

Each of the components of the negative electronic conduction pathway may be characterized by its composition, electrical properties, chemical properties, geometric and structural properties, etc. For example, in certain embodiments, each element of the pathway has the same composition (e.g., zinc or zinc coated copper). In other embodiments, at least two of the elements have different compositions.

As indicated, an element of the conductive pathway that is the subject of this application is the carrier or substrate for the negative electrode, which also serves as a current collector. Among the criteria to consider when choosing a material and structure for the substrate are electrochemically compatible with the negative electrode materials, cost, ease of coating (with the negative electrode material), suppression of hydrogen evolution, and ability to facilitate electron transport between the electrochemically active electrode material and the current collector.

As explained, the current collection substrate can be provided in various structural forms including perforated metal sheets, expanded metals, metal foams, etc. In a specific embodiment, the substrate is a perforated sheet or an expanded metal made from a zinc based material such as zinc coated copper or zinc coated copper alloy. In certain embodiments, the substrate is a perforated sheet having a thickness between about 2 and 5 mils. In certain embodiments, the substrate is an expanded metal having a thickness between about 2 and 20

mils. In other embodiments, the substrate is a metal foam having a thickness of between about 15 and 60 mils. In a specific embodiment, the carrier is about 3-4 mils thick perforated zinc coated copper. A specific range for the thickness of the negative electrode, including the carrier metal and negative electrode material is about 10 to 24 mils. Other components of the negative pathway, such as a negative current collector disk and cap, may be made from any of the base metals identified above for the current collection substrate. The base material chosen for the disk and/or cap should be highly conductive and inhibit the evolution of hydrogen, etc.

In certain embodiments, one or both of the disk and the cap employs zinc or a zinc alloy as a base metal. In certain embodiments, the current collector disk and/or the cap is a copper or copper alloy coated with zinc or an alloy of zinc containing, e.g., tin, silver, indium, lead, or a combination thereof. It may be desirable to pre-weld the current collector disk and jelly roll or employ a jelly roll that is an integral part of the current collector disk and tab that could be directly welded to the top. Such embodiments may find particular value in relatively low rate applications. These embodiments are particularly useful when the collector disk contains zinc.

The jelly roll may include a tab welded to one side of the negative electrode to facilitate contact with the collector disk.

It has been found that regular vent caps without proper anti-corrosion plating (e.g., tin, lead, silver, zinc, indium, etc.) can cause zinc to corrode during storage, resulting in leakage, gassing, and reduced shelf life. Note that if it is the can, rather than the cap, that is used as the negative terminal, then the can may be constructed from the materials identified above.

In some cases, the entire negative electronic pathway (including the terminal and one or more current collection elements) is made from the same material, e.g., zinc or copper coated with zinc. In a specific embodiment, the entire electronic pathway from the negative electrode to the negative terminal (current collector substrate, current collector disk, tab, and cap) is zinc plated copper or brass.

Some details of the structure of a vent cap and current collector disk, as well as the carrier substrate itself, are found in the following patent applications which are incorporated herein by reference for all purposes: PCT/US2006/015807 filed April 25, 2006 and PCT/US2004/026859 filed August 17, 2004 (publication WO 2005/020353 A3).

The Positive Electrode The positive electrode generally includes an electrochemically active nickel oxide or hydroxide and one or more additives to facilitate manufacturing, electron transport, wetting, mechanical properties, etc. For example, a positive electrode formulation may include at least an electrochemically active nickel oxide or hydroxide (e.g., nickel hydroxide (Ni(0H)2)), zinc oxide, cobalt oxide (CoO), cobalt metal, nickel metal, and a flow control agent such as carboxymethyl cellulose (CMC). Note that the metallic nickel and cobalt may be chemically pure or alloys. In certain embodiments, the positive electrode has a composition similar to that employed to fabricate the nickel electrode in a conventional nickel cadmium battery, although there may be some important optimizations for the nickel zinc battery system. A nickel foam matrix is preferably used to support the electroactive nickel (e.g., Ni(OH) 2) electrode material. In one example, commercially available nickel foam by Inco, Ltd. may be used. The diffusion path to the Ni(OH) 2 (or other electrochemically active material) through the nickel foam should be short for applications requiring high discharge rates. At high rates, the time it takes ions to penetrate the nickel foam is important. The width of the positive electrode, comprising nickel foam filled with the Ni(OH) 2 (or other electrochemically active material) and other electrode materials, should be optimized so that the nickel foam provides sufficient void space for the Ni(OH) 2 material while keeping the diffusion path of the ions to the Ni(OH) 2 through the foam short. The foam substrate thickness may be may be between 15 and 60 mils. In a preferred embodiment, the thickness of the positive electrode, comprising nickel foam filled with the electrochemically active and other electrode materials, ranges from about 16 - 24 mils. In a particularly preferred embodiment, positive electrode is about 20 mils thick.

The density of the nickel foam should be optimized to ensure that the electrochemically active material uniformly penetrates the void space of the foam. In a preferred embodiment, nickel foam of density ranging from about 300 - 500 g/m 2 is used. An even more preferred range is between about 350 - 500 g/m 2. In a particularly preferred embodiment nickel foam of density of about 350 g/m 2 is used. As the width of the electrode layer is decreased, the foam may be made less dense to ensure there is sufficient void space.

2 In a preferred embodiment, a nickel foam density of about 350 g/m and thickness ranging from about 16 - 18 mils is used.

The Separator A separator serves to mechanically isolate the positive and negative electrodes, while allowing ionic exchange to occur between the electrodes and the electrolyte. The separator also blocks zinc dendrite formation. Dendrites are crystalline structures having a skeletal or tree-like growth pattern ("dendritic growth") in metal deposition. In practice, dendrites form in the

conductive media of a power cell during the lifetime of the cell and effectively bridge the negative and positive electrodes causing shorts and subsequent loss of battery function.

Typically, a separator will have small pores. In certain embodiments described herein, the separator includes multiple layers. The pores and/or laminate structure may provide a tortuous path for zinc dendrites and therefore effectively bar penetration and shorting by dendrites.

Preferably, the porous separator has a tortuosity of between about 1.5 and 10, more preferably between about 2 and 5. The average pore diameter is preferably at most about 0.2 microns, and more preferably between about 0.02 and 0.1 microns. Also, the pore size is preferably fairly uniform in the separator. In a specific embodiment, the separator has a porosity of between about 35 and 55% with one preferred material having 45% porosity and a pore size of 0.1 micron.

In a preferred embodiment, the separator comprises at least two layers (and preferably exactly two layers) - a barrier layer to block zinc penetration and a wetting layer to keep the cell wet with electrolyte, allowing ionic exchange. This is generally not the case with nickel cadmium cells, which employ only a single separator material between adjacent electrode layers.

Performance of the cell may be aided by keeping the positive electrode as wet as possible and the negative electrode relatively dry. Thus, in some embodiments, the barrier layer is located adjacent to the negative electrode and the wetting layer is located adjacent to the positive electrode. This arrangement improves performance of the cell by maintaining electrolyte in intimate contact with the positive electrode.

In other embodiments, the wetting layer is placed adjacent to the negative electrode and the barrier layer is placed adjacent to the positive electrode. This arrangement aids recombination of oxygen at the negative electrode by facilitating oxygen transport to the negative electrode via the electrolyte.

The barrier layer is typically a microporous membrane. Any microporous membrane that is ionically conductive may be used. Often a polyolefin having a porosity of between about 30 and 80 per cent, and an average pore size of between about 0.005 and 0.3 micron will be suitable.

In a preferred embodiment, the barrier layer is a microporous polypropylene. The barrier layer is typically about 0.5 - 4 mils thick, more preferably between about 1.5 and 4 mils thick.

The wetting layer may be made of any suitable wettable separator material. Typically the wetting layer has a relatively high porosity e.g., between about 50 and 85% porosity. Examples include polyamide materials such as nylon-based as well as wettable polyethylene and polypropylene materials. In certain embodiments, the wetting layer is between about 1 and 10 mils thick, more preferably between about 3 and 6 mils thick. Examples of separate materials that may be employed as the wetting material include NKK VLlOO (NKK Corporation, Tokyo, Japan), Freudenberg FS2213E, Scimat 650/45 (SciMAT Limited, Swindon, UK), and Vilene FV4365. Other separator materials known in the art may be employed. As indicated, nylon-based materials and microporous polyolefins (e.g., polyethylenes and polypropylenes) are very often suitable.

The Electrolyte The electrolyte should possess a composition that limits dendrite formation and other forms of material redistribution in the zinc electrode. Such electrolytes have generally eluded the art.

But one that appears to meet the criterion is described in U.S. Patent No. 5,215,836 issued to M. Eisenberg on June 1, 1993, which is hereby incorporated by reference. A particularly preferred electrolyte includes (1) an alkali or earth alkali hydroxide present in an amount to produce a stoichiometric excess of hydroxide to acid in the range of about 2.5 to 11 equivalents per liter, (2) a soluble alkali or earth alkali fluoride in an amount corresponding to a concentration range of about 0.01 to 1 equivalents per liter of total solution, and (3) a borate, arsenate, and/or phosphate salt (e.g., potassium borate, potassium metaborate, sodium borate, sodium metaborate, and/or a sodium or potassium phosphate). In one specific embodiment, the electrolyte comprises about 4.5 to 10 equiv/liter of potassium hydroxide, from about 2 to 6 equiv/liter boric acid or sodium metaborate and from about 0.01 to 1 equivalents of potassium fluoride. A specific preferred electrolyte for high rate applications comprises about 8.5 equiv/liter of hydroxide, about 4.5 equivalents of boric acid and about 0.2 equivalents of potassium fluoride.

The invention is not limited to the electrolyte compositions presented in the Eisenberg patent.

Generally, any electrolyte composition meeting the criteria specified for the applications of interest will suffice. Assuming that high power applications are desired, then the electrolyte should have very good conductivity. Assuming that long cycle life is desired, then the electrolyte should resist dendrite formation. In the present invention, the use of borate and/or fluoride containing KOH electrolyte along with appropriate separator layers reduces the formation of dendrites thus achieving a more robust and long-lived power cell.

In a specific embodiment, the electrolyte composition includes an excess of between about 3 and 5 equiv/liter hydroxide (e.g., KOH, NaOH, and/or LiOH). This assumes that the negative electrode is a zinc oxide based electrode. For calcium zincate negative electrodes, alternate electrolyte formulations may be appropriate. In one example, an appropriate electrolyte for

calcium zincate has the following composition: about 15 to 25% by weight KOH, about 0.5 to 5.0% by weight LiOH. According to various embodiments, the electrolyte may comprise a liquid and a gel. The gel electrolyte may comprise a thickening agent such as CARBOPOL速 available from Noveon of Cleveland, OH. In a preferred embodiment, a fraction of the active electrolyte material is in gel form. In a specific embodiment, about 5-25% by weight of the electrolyte is provided as gel and the gel component comprises about 1-2% by weight CARBOPOL速.

In some cases, the electrolyte may contain a relatively high concentration of phosphate ion as discussed in US Patent Application No. 11/346,861, filed February 1, 2006 and incorporated herein by reference for all purposes.

Although various details have been omitted for clarity's sake, various design alternatives may be implemented. Therefore, the present examples are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the invention.

2008036948 Claims What is claimed is: 1. A method of charging a nickel-zinc battery comprising: measuring a temperature of the battery, calculating a calculated voltage based on at least the temperature of the battery, charging the battery at a constant current until a measured battery voltage is the same as the calculated voltage, charging the battery at a calculated voltage per nickel-zinc cell, and stopping the battery charging at the calculated voltage per cell when an end-of- charge condition is satisfied; wherein the battery comprises one or more cells.

2. The method of claim 1, wherein the constant current is about 1-2 amps per 2 Amp hour of capacity in the battery. 3. The method of claim 1, wherein the constant current charging operation increases a capacity of the battery to about 80%.

4. The method of claim 1, further comprising: charging the battery at a corrective current to correct cell imbalance after charging the battery at the calculated voltage. 5. The method of claim 1, further comprising: charging the battery at a minimum current to maintain charge during period when the battery is not in use and the end-of-charge condition has been satisfied.

6. The method of claim 1, further comprising: charging the battery at an initial current until a start-of-charge condition is satisfied. 7. The method of claim 4, wherein the corrective current is about 50-200 milliamps per 2 Amp hour of capacity in the battery.

8. The method of claim 5, wherein the minimum current is about 0-50 milliamps per 2 Amp hour of capacity in the battery.

9. The method of claim 6, wherein the initial current is about 0-50 milliamps per 2 Amp hour of capacity in the battery.

10. The method of claim 1, wherein the end-of-charge condition is selected from the group consisting of: a charging current of less than a defined current associated with a specified state-of- charge; a lapse of 1.5 hours of charging at the calculated voltage; a battery temperature increase of 15 degrees Celsius; a charging current of more than about a defined threshold associated with a short circuit in the batery; and, combinations thereof.

11. The method of claim 6, wherein the start-of charge condition is selected from the group consisting of: (a) a battery temperature of 15 degrees Celsius; (b) a battery voltage of about 1 volt per cell; and, (c) a lapse of about 20 hours or more without meeting either of conditions (a) or (b).

12. The method of claim 1, further comprising repeating the measuring, and calculating during the charging.

13. A nickel-zinc battery charger comprising: an enclosure for holding the nickel-zinc battery, a thermistor configured to thermally couple to a battery during operation; and, a controller configured to execute a set of instructions, the instructions comprising instructions to: measure a temperature of the battery, calculate a calculated voltage, charge the battery at a constant current until a measured battery voltage equals the calculated voltage, charge the battery at the calculated voltage, and stop the charge at the calculated voltage when an end-of-charge condition is detected.

14. The battery charger of claim 13, further comprising: a recondition button and wherein the instructions further comprises charging the battery at an initial current when the recondition button is pressed.

15. The battery charger of claim 13, wherein the instructions further comprises instructions to charge the battery at a corrective current. 16. The battery charger of claim 13, wherein the instructions further comprises instructions to charge the battery at a minimum current.

17. A method of correcting nickel-zinc battery cell imbalance comprising: providing a battery pack at greater than about 90% state-of-charge in a charger, and charging the battery at a corrective current for about 30 minutes to 2 hours without limiting the voltage.

18. The method of claim 17, wherein the corrective current is about 50-200 milliamps per 2

Amp hour of capacity in the battery. 19. The method of claim 17, further comprising: charging the battery at a minimum current until the battery is removed from the charger.

20. The method of claim 19, wherein the minimum current is 0-50 milliamps per 2 Amp hour of capacity in the battery. 21. A method of charging a battery comprising: measuring a temperature of the battery, measuring a voltage of the battery, calculating a calculated voltage based on at least the temperature of the battery, charging the battery at a charge current until the battery voltage equals the calculated voltage, reducing the charging current by a defined factor, charging the battery at the reduced charge current until the battery voltage equals the calculated voltage, wherein the factor is about 2-10.

22. The method of claim 21, further comprising repeating the reducing and charging the battery at the reduced charge operations to the same voltage level. 23. A method of charging a nickel-zinc cell, the method comprising: (a) charging the nickel-zinc battery at a constant current until reaching a point at which (i) the cell's state of charge is at least about 70%, (ii) a nickel electrode of the cell has not yet begun to evolve oxygen at a substantial level, and (iii) the cell voltage is between about 1.88 and 1.93 volts; and (b) charging the nickel-zinc battery at a constant voltage in the range of 1.88-1.93 until an end-of-charge condition is satisfied.

24. The method of claim 23, wherein charging the battery at a constant current is conducted at a current of up to about 4 Amps per 2 Amp hour battery capacity, and wherein the nickel-zinc "1 ~ battery employs an electrolyte having a conductivity of at least about 0.5 cm ohm \ 25. The method of claim 24, wherein charging t he battery at a constant current is conducted until the cell voltage is between about 1.88 and 1.91 volts.

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NT OF J US

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Office of Justice Programs

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U.S. Department of Justice

IJ J O F OJJ D P B RO J US T I C E P

National Institute of Justice

National Institute of Justice Law Enforcement and Corrections Standards and Testing Program

NEW TECHNOLOGY BATTERIES GUIDE NIJ Guide 200-98

ABOUT THE LAW ENFORCEMENT AND CORRECTIONS STANDARDS AND TESTING PROGRAM The Law Enforcement and Corrections Standards and Testing Program is sponsored by the Office of Science and Technology of the National Institute of Justice (NIJ), U.S. Department of Justice. The program responds to the mandate of the Justice System Improvement Act of 1979, which created NIJ and directed it to encourage research and development to improve the criminal justice system and to disseminate the results to Federal, State, and local agencies.

The Law Enforcement and Corrections Standards and Testing Program is an applied research effort that determines the technological needs of justice system agencies, sets minimum performance standards for specific devices, tests commercially available equipment against those standards, and disseminates the standards and the test results to criminal justice agencies nationally and internationally.

The program operates through: The Law Enforcement and Corrections Technology Advisory Council (LECTAC) consisting of nationally recognized criminal justice practitioners from Federal, State, and local agencies, which assesses technological needs and sets priorities for research programs and items to be evaluated and tested.

The Office of Law Enforcement Standards (OLES) at the National Institute of Standards and Technology, which develops voluntary national performance standards for compliance testing to ensure that individual items of equipment are suitable for use by criminal justice agencies. The standards are based upon laboratory testing and evaluation of representative samples of each item of equipment to determine the key attributes, develop test methods, and establish minimum performance requirements for each essential attribute. In addition to the highly technical standards, OLES also produces technical reports and user guidelines that explain in nontechnical terms the capabilities of available equipment.

The National Law Enforcement and Corrections Technology Center (NLECTC), operated by a grantee, which supervises a national compliance testing program conducted by independent laboratories. The standards developed by OLES serve as performance benchmarks against which commercial equipment is measured. The facilities, personnel, and testing capabilities of the independent laboratories are evaluated by OLES prior to testing each item of equipment, and OLES helps the NLECTC staff review and analyze data. Test results are published in Equipment Performance Reports designed to help justice system procurement officials make informed purchasing decisions.

Publications are available at no charge from the National Law Enforcement and Corrections Technology Center.

Some documents are also available online through the Internet/World Wide Web. To request a document or additional information, call 800-248-2742 or 301-519-5060, or write: National Law Enforcement and Corrections Technology Center P.O. Box 1160 Rockville, MD 20849-1160 E-mail: asknlectc@nlectc.org World Wide Web address: http://www.nlectc.org

The National Institute of Justice is a component of the Office of Justice Programs, which also includes the Bureau of Justice Assistance, Bureau of Justice Statistics, Office of Juvenile Justice and Delinquency Prevention, and the Office for Victims of Crime.

National Institute of Justice

Jeremy Travis Director

The Technical effort to develop this Guide was conducted under Interagency Agreement 94-IJ-R-004 Project No. 97-027-CTT.

This Guide was prepared by the Office of Law Enforcement Standards (OLES) of the National Institute of Standards and Technology (NIST) under the direction of A. George Lieberman, Program Manager for Communications Systems, and Kathleen M. Higgins, Director of OLES. The work resulting in this guide was sponsored by the National Institute of Justice, David G. Boyd, Director, Office of Science and Technology.

New Technology Batteries Guide

FOREWORD The Office of Law Enforcement Standards (OLES) of the National Institute of Standards and Technology furnishes technical support to the National Institute of Justice program to strengthen law enforcement and criminal justice in the United States. OLESâ&#x20AC;&#x2122;s function is to conduct research that will assist law enforcement and criminal justice agencies in the selection and procurement of quality equipment.

OLES is: (1) subjecting existing equipment to laboratory testing and evaluation, and (2) conducting research leading to the development of several series of documents, including national standards, user guides, and technical reports.

This document covers research conducted by OLES under the sponsorship of the National Institute of Justice. Additional reports as well as other documents are being issued under the OLES program in the areas of protective clothing and equipment, communications systems, emergency equipment, investigative aids, security systems, vehicles, weapons, and analytical techniques and standard reference materials used by the forensic community.

Technical comments and suggestions concerning this report are invited from all interested parties. They may be addressed to the Director, Office of Law Enforcement Standards, National Institute of Standards and Technology, Gaithersburg, MD 20899.

David G. Boyd, Director Office of Science and Technology National Institute of Justice

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BACKGROUND The Office of Law Enforcement Standards conventional format, that details the (OLES) was established by the National performance that the equipment is required to Institute of Justice (NIJ) to provide focus on two give, and describes test methods by which its major objectives: (1) to find existing equipment actual performance can be measured. These which can be purchased today, and (2) to requirements are technical, and are stated in develop new law-enforcement equipment which terms directly related to the equipment’s use. can be made available as soon as possible. A The basic purposes of a standard are (1) to be a part of OLES’s mission is to become thoroughly reference in procurement documents created by familiar with existing equipment, to evaluate its purchasing officers who wish to specify performance by means of objective laboratory equipment of the “standard” quality, and (2) to tests, to develop and identify objectively improve these equipment of methods of test, to acceptable develop performance A standard is not intended to inform performance. standards for and guide the reader; that is the selected equipment Note that a standard function of a guideline items, and to prepare is not intended to guidelines for the inform and guide the selection and use of reader; that is the this equipment. All of these activities are function of a “guideline.” Guidelines are written directed toward providing law enforcement in non-technical language and are addressed to agencies with assistance in making good the potential user of the equipment. They equipment selections and acquisitions in include a general discussion of the equipment, accordance with their own requirements. its important performance attributes, the various models currently on the market, objective test As the OLES program has matured, there has data where available, and any other information been a gradual shift in the objectives of the that might help the reader make a rational OLES projects. The initial emphasis on the selection among the various options or development of standards has decreased, and the alternatives available to him or her. emphasis on the development of guidelines has increased. For the significance of this shift in This battery guide is provided to inform the emphasis to be appreciated, the precise reader of the latest technology related to battery definitions of the words “standard” and composition, battery usage, and battery charging “guideline” as used in this context must be techniques. clearly understood.

Kathleen Higgins A “standard” for a particular item of equipment National Institute of Standards and Technology is understood to be a formal document, in a March 27, 1997

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CONTENTS page FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . v CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii List of Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . viii 1. Fundamentals of Battery Technology . . . . . . . . . .

1.1 What is a Battery? . . . . . . . . . . . . . . . . . . . . .

1.2 How Does a Battery Work? . . . . . . . . . . . . . .

1.3 Galvanic Cells vs. Batteries . . . . . . . . . . . . . .

1.4 Primary Battery . . . . . . . . . . . . . . . . . . . . . . .

1.5 Secondary Battery . . . . . . . . . . . . . . . . . . . . .

1.6 Battery Labels . . . . . . . . . . . . . . . . . . . . . . . .

1 1 1 3 3 3 3

2. Available Battery Types . . . . . . . . . . . . . . . . . . . . 5 2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1.1 Acid vs. Alkaline . . . . . . . . . . . . . . . . . 5 2.1.2 Wet vs. Dry . . . . . . . . . . . . . . . . . . . . . 5 2.1.3 Categories . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Vehicular Batteries . . . . . . . . . . . . . . . . . . . . 6 2.2.1 Lead-Acid ................... 6 2.2.2 Sealed vs. Flooded . . . . . . . . . . . . . . . 6 2.2.3 Deep-Cycle Batteries . . . . . . . . . . . . . . 7 2.2.4 Battery Categories for Vehicular Batteries . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3 “Household” Batteries . . . . . . . . . . . . . . . . . . 7 2.3.1 Zinc-carbon (Z-C) . . . . . . . . . . . . . . . . 8 2.3.2 Zinc-Manganese Dioxide Alkaline Cells (“Alkaline Batteries”) . . . . . . . . . . . . . 8 2.3.3 Rechargeable Alkaline Batteries . . . . . 9 2.3.4 Nickel-Cadmium (Ni-Cd) . . . . . . . . . . 9 2.3.5 Nickel-Metal Hydride (Ni-MH) . . . . 10 2.3.6 Nickel-Iron (Ni-I) . . . . . . . . . . . . . . . 10

2.3.7 Nickel-Zinc (Ni-Z) . . . . . . . . . . . . . .

2.3.8 Lithium and Lithium Ion . . . . . . . . . .

2.4 Specialty Batteries (“Button” and Miniature Batteries) . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.4.1 Metal-Air Cells . . . . . . . . . . . . . . . . .

2.4.2 Silver Oxide . . . . . . . . . . . . . . . . . . .

2.4.3 Mercury Oxide . . . . . . . . . . . . . . . . .

2.5 Other Batteries . . . . . . . . . . . . . . . . . . . . . . .

2.5.1 Nickel-Hydrogen (Ni-H) . . . . . . . . . .

2.5.2 Thermal Batteries . . . . . . . . . . . . . . .

2.5.3 Super Capacitor . . . . . . . . . . . . . . . . .

2.5.4 The Potato Battery . . . . . . . . . . . . . . .

2.5.5 The Sea Battery . . . . . . . . . . . . . . . . .

2.5.6 Other Developments . . . . . . . . . . . . .

10 10

3. Performance, Economics and Tradeoffs . . . . . . .

3.1 Energy Densities . . . . . . . . . . . . . . . . . . . . .

3.2 Energy per Mass . . . . . . . . . . . . . . . . . . . . .

3.3 Energy Per Volume . . . . . . . . . . . . . . . . . . .

3.4 Memory Effects . . . . . . . . . . . . . . . . . . . . . .

3.5 Voltage Profiles . . . . . . . . . . . . . . . . . . . . . .

3.6 Self-Discharge Rates . . . . . . . . . . . . . . . . . .

3.7 Operating Temperatures . . . . . . . . . . . . . . .

3.8 Cycle Life . . . . . . . . . . . . . . . . . . . . . . . . . .

3.9 Capacity Testing . . . . . . . . . . . . . . . . . . . . .

3.10 Battery Technology Comparison . . . . . . . .

15 15 15 15 16 16 17 17 18 18 18

4. Selecting the Right Battery for the Application .

4.1 Battery Properties . . . . . . . . . . . . . . . . . . . .

4.2 Environmental Concerns . . . . . . . . . . . . . . .

4.3 Standardization . . . . . . . . . . . . . . . . . . . . . .

4.4 Testing Capacities . . . . . . . . . . . . . . . . . . . .

4.5 Mobile Radios . . . . . . . . . . . . . . . . . . . . . . .

4.6 Cellular Phones and PCS Phones . . . . . . . .

4.7 Laptop Computers . . . . . . . . . . . . . . . . . . . .

4.8 Camcorders . . . . . . . . . . . . . . . . . . . . . . . . .

4.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .

23 24 24 26 26 27 27 28 28 29

12 12 12 13 13 13 13 13 14 14 14

5. Battery Handling and Maintenance . . . . . . . . . . . 31 5.1 Battery Dangers . . . . . . . . . . . . . . . . . . . . . . 31 5.2 Extending Battery Life . . . . . . . . . . . . . . . . 33

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List of Figures 6. Battery Chargers and Adapters . . . . . . . . . . . . . .

6.1 Battery Chargers . . . . . . . . . . . . . . . . . . . . .

6.2 Charge Rates . . . . . . . . . . . . . . . . . . . . . . . .

6.3 Charging Techniques . . . . . . . . . . . . . . . . . .

6.4 Charging Lead-Acid Batteries . . . . . . . . . . .

6.5 Charging Ni-Cd Batteries . . . . . . . . . . . . . .

6.6 Timed-Charge Charging . . . . . . . . . . . . . . .

6.7 Pulsed Charge-Discharge Chargers . . . . . . .

6.8 Charging Button Batteries . . . . . . . . . . . . . .

6.9 Internal Chargers . . . . . . . . . . . . . . . . . . . . .

6.10 Battery Testers . . . . . . . . . . . . . . . . . . . . . .

6.11 “Smart” Batteries . . . . . . . . . . . . . . . . . . . .

6.12 End of Life . . . . . . . . . . . . . . . . . . . . . . . .

6.13 Battery Adapters . . . . . . . . . . . . . . . . . . . .

35 35 36 36 36 37 37 38 38 38 38 39 39 40

7. Products and Suppliers . . . . . . . . . . . . . . . . . . . .

7.1 Battery Manufacturers . . . . . . . . . . . . . . . . .

7.1.1 Battery Engineering . . . . . . . . . . . . . .

7.1.2 Duracell . . . . . . . . . . . . . . . . . . . . . . .

7.1.3 Eveready . . . . . . . . . . . . . . . . . . . . . .

7.1.4 Rayovac . . . . . . . . . . . . . . . . . . . . . . .

41 41 42 42 42 42

8. A Glossary of Battery Terms . . . . . . . . . . . . . . . 43 9. Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

page Figure 1. Conceptual diagram of a galvanic cell. . . . 1 Figure 2. Energy densities, W#h/kg, of various battery types (adapted from NAVSO P-3676). . . . . . . . 15 Figure 3. Energy densities, W#h/L, of various battery types (adapted from NAVSO P-3676). . . . . . . . 16 Figure 4. Flat discharge curve vs. sloping discharge curve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 5. Performance comparison of primary and secondary alkaline and Ni-Cd batteries (adapted from Design Note: Renewable Reusable Alkaline Batteries). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 List of Tables page Table 1. The Electromotive Series for Some Battery Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Table 2. Various Popular Household-Battery Sizes . 8 Table 3. Battery Technology Comparison (adapted from Design Note: Renewable Reusable Alkaline Batteries) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Table 4. A Comparison of Several Popular Battery Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table 5. Recommended Battery Types for Various Usage Conditions . . . . . . . . . . . . . . . . . . . . . . . . 25 Table 6. Typical Usage of Portable Telecommunications Equipment. . . . . . . . . . . . . 27 Table 7. Charge Rate Descriptions . . . . . . . . . . . . . 35 Table 8. Some On-Line Information Available via the World Wide Web . . . . . . . . . . . . . . . . . . . . . . . . 41 List of Equations page Equation 1. The chemical reaction in a lead-acid battery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Equation 2. The chemical reaction in a Leclanché cell. ....................................... 8 Equation 3. The chemical reaction in a nickelcadmium battery. . . . . . . . . . . . . . . . . . . . . . . . . . 9 Equation 4. The chemical reaction in a lithiummanganese dioxide cell. . . . . . . . . . . . . . . . . . . . 11

viii

New Technology Batteries Guide

COMMONLY USED SYMBOLS AND ABBREVIATIONS A ac AM cd cm CP c/s d dB dc (C (F dia emf eq F fc fig.

FM ft ft/s g g gr

ampere alternating current amplitude modulation candela centimeter chemically pure cycle per second day decibel direct current degree Celsius degree Fahrenheit diameter electromotive force equation farad footcandle figure frequency modulation foot foot per second acceleration/gravity gram grain

H h hf Hz i.d. in ir J L L lb lbf lbf#in lm ln log M m min mm mph m/s N N #m

henry hour high frequency hertz (c/s) inside diameter inch infrared joule lambert liter pound pound-force pound-force inch lumen logarithm (natural) logarithm (common) molar meter minute millimeter mile per hour meter per second newton newton meter

nm No. o.d.

6

p.

Pa pe pp. ppm qt rad rf rh s SD sec.

SWR uhf uv V vhf W

wt

nanometer number outside diameter ohm page pascal probable error pages part per million quart radian radio frequency relative humidity second standard deviation section standing wave ratio ultrahigh frequency ultraviolet volt very high frequency watt wavelength weight

area=unit2 (e.g., ft2, in2, etc.); volume=unit3 (e.g., ft2, m3, etc.)

PREFIXES d c m Âľ n p

deci (10-1) centi (10-2) milli (10-3) micro (10-6) nano (10-9) pico (10-12)

da h k M G T

deka (10) hecto (102) kilo (103) mega (106) giga (109) tera (1012)

COMMON CONVERSIONS (See ASTM E380) ft/sĂ&#x2014;0.3048000=m/s ftĂ&#x2014;0.3048=m ft#lbfĂ&#x2014;1.355818=J grĂ&#x2014;0.06479891=g inĂ&#x2014;2.54=cm kWhĂ&#x2014;3600000=J

lbĂ&#x2014;0.4535924=kg lbfĂ&#x2014;4.448222=N lbf/ftĂ&#x2014;14.59390=N/m lbf#inĂ&#x2014;0.1129848=N #m lbf/in2Ă&#x2014;6894.757=Pa mph1.609344=km/h qtĂ&#x2014;0.9463529=L #

Temperature: (T F 32)Ă&#x2014;5/9=T C Temperature: (T CĂ&#x2014;C9/5)+32=T F (

(

(

(

ix

New Technology Batteries Guide

x

1. Fundamentals of Battery Technology wires connect the electrodes to an electrical load (a light bulb in this case). The metal in A battery, in concept, can be any device that the anode (the negative terminal) oxidizes stores energy for later use. A rock, pushed to (i.e., it “rusts”), releasing negatively charged the top of a hill, can be considered a kind of electrons and positively charged metal ions. battery, since the energy used to push it up the The electrons travel through the wire (and the hill (chemical energy, from muscles or electrical load) to the cathode (the positive combustion engines) is converted and stored terminal). The electrons combine with the as potential kinetic energy at the top of the material in the cathode. This combination hill. Later, that energy is released as kinetic process is called reduction, and it releases a and thermal energy when the rock rolls down negatively charged metal-oxide ion. At the the hill. interface with the electrolyte, this ion Common use of the causes a water word, “battery,” molecule to split however, is limited into a hydrogen ion to an electroand a hydroxide chemical device ion. The positively that converts charged hydrogen chemical energy ion combines with into electricity, by the negatively use of a galvanic charged metalcell. A galvanic cell oxide ion and is a fairly simple becomes inert. The device consisting of negatively charged two electrodes (an hydroxide ion anode and a Figure 1. Conceptual diagram of a galvanic cell. flows through the cathode) and an electrolyte to the electrolyte solution. Batteries consist of one or anode where it combines with the positively more galvanic cells. charged metal ion, forming a water molecule and a metal-oxide molecule.

1.2 HOW DOES A BATTERY WORK? 1.1 WHAT IS A BATTERY?

Figure 1 shows a simple galvanic cell.

Electrodes (two plates, each made from a different kind of metal or metallic compound) are placed in an electrolyte solution. External

In effect, metal ions from the anode will “dissolve” into the electrolyte solution while hydrogen molecules from the electrolyte are deposited onto the cathode.

1

New Technology Batteries Guide

When the anode is fully oxidized or the cathode is fully reduced, the chemical reaction will stop and the battery is considered to be discharged.

Recharging a battery is usually a matter of externally applying a voltage across the plates to reverse the chemical process. Some chemical reactions, however, are difficult or impossible to reverse. Cells with irreversible reactions are commonly known as primary cells, while cells with reversible reactions are known as secondary cells. It is dangerous to attempt to recharge primary cells.

The amount of voltage and current that a galvanic cell produces is directly related to the types of materials used in the electrodes and electrolyte. The length of time the cell can produce that voltage and current is related to the amount of active material in the cell and the cellâ&#x20AC;&#x2122;s design.

Every metal or metal compound has an electromotive force, which is the propensity of the metal to gain or lose electrons in relation to another material. Compounds with a positive electromotive force will make good anodes and those with a negative force will make good cathodes. The larger the difference between the electromotive forces of the anode and cathode, the greater the amount of energy that can be produced by the cell. Table 1 shows the electromotive force of some common battery components.

2

Table 1. The Electromotive Series for Some Battery Components Anode Materials (Listed from worst [most positive] to best [most negative])

Cathode Materials (Listed from best [most positive] to worst [most negative])

Gold

Ferrate

Platinum

Iron Oxide

Mercury

Cuprous Oxide

Palladium

Iodate

Silver

Cupric Oxide

Copper

Mercuric Oxide

Hydrogen

Cobaltic Oxide

Lead

Manganese Dioxide

Tin

Lead Dioxide

Nickel

Silver Oxide

Iron

Oxygen

Chromium

Nickel Oxyhydroxide

Zinc

Nickel Dioxide

Aluminum

Silver Peroxide

Magnesium

Permanganate

Lithium

Bromate

Over the years, battery specialists have experimented with many different combinations of material and have generally tried to balance the potential energy output of a battery with the costs of manufacturing the battery. Other factors, such as battery weight, shelf life, and environmental impact, also enter into a batteryâ&#x20AC;&#x2122;s design.

New Technology Batteries Guide

1.3 GALVANIC CELLS VS. BATTERIES From earlier discussion, we know that a battery is one or more galvanic cells connected in series or in parallel.

A battery composed of two 1.5 V galvanic cells connected in series, for example, will produce 3 V. A typical 9 V battery is simply six 1.5 V cells connected in series. Such a series battery, however, will produce a current that is the equivalent to just one of the galvanic cells.

diminished capacity), it is more likely that the battery will simply fail to hold any charge, will leak electrolyte onto the battery charger, or will overheat and cause a fire. It is unwise and dangerous to recharge a primary battery.

1.5 SECONDARY BATTERY A secondary battery is commonly known as a rechargeable battery. It is usually designed to have a lifetime of between 100 and 1000 recharge cycles, depending on the composite materials.

A battery composed of two 1.5 V galvanic Secondary batteries are, generally, more cost cells connected in parallel, on the other hand, effective over time than primary batteries, will still produce a since the battery voltage of 1.5 V, can be recharged but the current and reused. A A battery is one or more galvanic provided can be single discharge cells connected in series or in double the current cycle of a primary parallel that just one cell battery, however, would create. Such will provide more a battery can current for a longer provide current twice as long as a single cell. period of time than a single discharge cycle of an equivalent secondary battery.

Many galvanic cells can be thus connected to create a battery with almost any current at any 1.6 BATTERY LABELS voltage level.

The American National Standards Institute (ANSI) Standard, ANSI C18.1M-1992, lists 1.4 PRIMARY BATTERY several battery features that must be listed on a A primary battery is a battery that is designed battery’s label. They are: to be cycled (fully discharged) only once and then discarded. Although primary batteries are _ Manufacturer -- The name of the battery often made from the same base materials as manufacturer. secondary (rechargeable) batteries, the design _ ANSI Number -- The ANSI/NEDA and manufacturing processes are not the same. number of the battery. _ Date -- The month and year that the battery Battery manufacturers recommend that was manufactured or the month and year that primary batteries not be recharged. Although the battery “expires” (i.e., is no longer attempts at recharging a primary battery will guaranteed by the manufacturer). occasionally succeed (usually with a _ Voltage -- The nominal battery voltage.

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New Technology Batteries Guide

_ Polarity -- The positive and negative terminals. The terminals must be clearly marked. _ Warnings -- Other warnings and cautions related to battery usage and disposal.

4

2. Available Battery Types 2.1 GENERAL 2.1.1 Acid vs. Alkaline Batteries are often classified by the type of electrolyte used in their construction. There are three common classifications: acid, mildly acid, and alkaline.

Acid-based batteries often use sulphuric acid as the major component of the electrolyte.

Automobile batteries are acid-based. The electrolyte used in mildly acidic batteries is far less corrosive than typical acid-based batteries and usually includes a variety of salts that produce the desired acidity level. Inexpensive household batteries are mildly acidic batteries.

Alkaline batteries typically use sodium hydroxide or potassium hydroxide as the main component of the electrolyte. Alkaline batteries are often used in applications where long-lasting, high-energy output is needed, such as cellular phones, portable CD players, radios, pagers, and flash cameras.

2.1.2 Wet vs. Dry “Wet” cells refer to galvanic cells where the electrolyte is liquid in form and is allowed to flow freely within the cell casing. Wet batteries are often sensitive to the orientation of the battery. For example, if a wet cell is oriented such that a gas pocket accumulates around one of the electrodes, the cell will not produce current. Most automobile batteries are wet cells.

“Dry” cells are cells that use a solid or powdery electrolyte. These kind of electrolytes use the ambient moisture in the air to complete the chemical process. Cells with liquid electrolyte can be classified as “dry” if the electrolyte is immobilized by some mechanism, such as by gelling it or by holding it in place with an absorbent substance such as paper.

In common usage, “dry cell” batteries will usually refer to zinc-carbon cells (Sec. 2.3.1) or zinc-alkaline-manganese dioxide cells (Sec. 2.3.2), where the electrolyte is often gelled or held in place by absorbent paper.

Some cells are difficult to categorize. For example, one type of cell is designed to be stored for long periods without its electrolyte present. Just before power is needed from the cell, liquid electrolyte is added.

2.1.3 Categories Batteries can further be classified by their intended use. The following sections discuss four generic categories of batteries; “vehicular” batteries (Sec. 2.2), “household” batteries (Sec. 2.3), “specialty” batteries (Sec. 2.4), and “other” batteries (Sec. 2.5). Each section will focus on the general properties of that category of battery.

Note that some battery types (acidic or alkaline, wet or dry) can fall into several different categories. For this guideline, battery types are placed into the category in which 5

New Technology Batteries Guide

they are most likely to be found in commercial usage.

Equation 1 shows the chemical reaction in a lead-acid cell.

2.2 VEHICULAR BATTERIES This section discusses battery types and configurations that are typically used in motor vehicles. This category can include batteries that drive electric motors directly or those that provide starting energy for combustion engines. This category will also include large, stationary batteries used as power sources for emergency building lighting, remote-site power, and computer back up.

Vehicular batteries are usually available off-theshelf in standard designs or can be custom built for specific applications.

Battery largest use for lead in the world.

Encyclopedia of Physical Science and Technology, Brooke Schumm, Jr., 1992.

6

Equation 1. The chemical reaction in a leadacid battery.

Lead-acid batteries remain popular because they can produce high or low currents over a wide range of temperatures, they have good shelf life and life cycles, and they are relatively inexpensive to manufacture. Leadacid batteries are usually rechargeable. manufacturing is the single

2.2.1 Lead-Acid Lead-acid batteries, developed in the late 1800s, were the first commercially practical batteries. Batteries of this type remain popular because they are relatively inexpensive to produce and sell. The most widely known uses of lead-acid batteries are as automobile batteries. Rechargeable lead-acid batteries have become the most widely used type of battery in the worldâ&#x20AC;&#x201D;more than 20 times the use rate of its nearest rivals. In fact, battery manufacturing is the single largest use for lead in the world.1

1

PbO2 Pb 2H2SO4 2PbSO4 2H2O

Lead-acid batteries come in all manner of shapes and sizes, from household batteries to large batteries for use in submarines. The most noticeable shortcomings of lead-acid batteries are their relatively heavy weight and their falling voltage profile during discharge (Sec. 3.5).

2.2.2 Sealed vs. Flooded In â&#x20AC;&#x153;floodedâ&#x20AC;? batteries, the oxygen created at the positive electrode is released from the cell and vented into the atmosphere. Similarly, the hydrogen created at the negative electrode is also vented into the atmosphere. The overall result is a net loss of water (H2O) from the cell. This lost water needs to be periodically replaced. Flooded batteries must be vented to prevent excess pressure from the build up of these gases. Also, the room or enclosure housing the battery must be vented, since a concentrated hydrogen and oxygen atmosphere is explosive.

New Technology Batteries Guide

In sealed batteries, however, the generated oxygen combines chemically with the lead and then the hydrogen at the negative electrode, and then again with reactive agents in the electrolyte, to recreate water. The net result is no significant loss of water from the cell.

2.2.3 Deep-Cycle Batteries Deep-cycle batteries are built in configurations similar to those of regular batteries, except that they are specifically designed for prolonged use rather than for short bursts of use followed by a short recycling period. The term “deep-cycle” is most often applied to lead-acid batteries. Deep-cycle batteries require longer charging times, with lower current levels, than is appropriate for regular batteries.

As an example, a typical automobile battery is usually used to provide a short, intense burst of electricity to the automobile’s starter. The battery is then quickly recharged by the automobile’s electrical system as the engine runs. The typical automobile battery is not a deep-cycle battery.

A battery that provides power to a recreational vehicle (RV), on the other hand, would be expected to power lights, small appliances, and other electronics over an extended period of time, even while the RV’s engine is not running. Deep-cycle batteries are more appropriate for this type of continual usage.

2.2.4

Battery Categories for Vehicular Batteries Vehicular, lead-acid batteries are further grouped (by typical usage) into three different categories:

8 Starting-Lighting-Ignition (SLI) -Typically, these batteries are used for short, quick-burst, high-current applications. An example is an automotive battery, which is expected to provide high current, occasionally, to the engine’s starter.

8 Traction -- Traction batteries must provide moderate power through many deep discharge cycles. One typical use of traction batteries is to provide power for small electric vehicles, such as golf carts. This type of battery use is also called Cycle Service.

8 Stationary -- Stationary batteries must have a long shelf life and deliver moderate to high currents when called upon. These batteries are most often used for emergencies.

Typical uses for stationary batteries are in uninteruptable power supplies (UPS) and for emergency lighting in stairwells and hallways.

This type of battery use is also called Standby or Float.

2.3 “HOUSEHOLD” BATTERIES “Household” batteries are those batteries that are primarily used to power small, portable devices such as flashlights, radios, laptop computers, toys, and cellular phones. The following subsections describe the technologies for many of the formerly used and presently used types of household batteries.

Typically, household batteries are small, 1.5 V cells that can be readily purchased off the shelf. These batteries come in standard shapes and sizes as shown in Table 2. They can also be custom designed and molded to fit any size battery compartment (e.g., to fit inside a cellular phone, camcorder, or laptop computer).

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New Technology Batteries Guide

Zn 2MnO2 2NH4Cl Zn(NH3)2Cl2 2MnOOH

Table 2. Various Popular Household-Battery Sizes Size

Shape and Dimensions

Voltage

D

Cylindrical, 61.5 mm tall, 34.2 mm diameter.

1.5 V

C

Cylindrical, 50.0 mm tall, 26.2 mm diameter.

1.5 V

AA

Cylindrical, 50.5 mm tall, 14.5 mm diameter.

1.5 V

AAA

Cylindrical, 44.5 mm tall, 10.5 mm diameter

1.5 V

9 Volt

Rectangular, 48.5 mm tall, 26.5 mm wide, 17.5 mm deep.

9V

Note: Three other standard sizes of household batteries are available, AAAA, N, and 6-V (lantern) batteries. It is estimated that 90% of portable, battery-operated devices require AA, C, or D battery sizes.

Most of the rest of this guideline will focus on designs, features, and uses of household batteries.

2.3.1 Zinc-carbon (Z-C) Zinc-carbon cells, also known as “Leclanché cells” are widely used because of their relatively low cost. Equation 2 shows the chemical reaction in a Leclanché cell. They were the first widely available household batteries. Zinc-carbon cells are composed of a manganese dioxide and carbon cathode, a zinc anode, and zinc chloride (or ammonium chloride) as the electrolyte.

8

Equation 2. The chemical reaction in a Leclanché cell.

Generally, zinc-carbon cells are not rechargeable and they have a sloping discharge curve (i.e., the voltage level decreases relative to the amount of discharge).

Zinc-carbon cells will produce 1.5 V, and they are mostly used for non-critical uses such as small household devices like flashlights and portable personal radios.

One notable drawback to these kind of batteries is that the outer, protective casing of the battery is made of zinc. The casing serves as the anode for the cell and, in some cases, if the anode does not oxidize evenly, the casing can develop holes that allow leakage of the mildly acidic electrolyte which can damage the device being powered.

2.3.2

Zinc-Manganese Dioxide Alkaline Cells (“Alkaline Batteries”) When an alkaline electrolyte—instead of the mildly acidic electrolyte—is used in a regular zinc-carbon battery, it is called an “alkaline” battery. An alkaline battery can have a useful life of five to six times that of a zinc-carbon battery. One manufacturer estimates that 30% of the household batteries sold in the world

New Technology Batteries Guide

today are zinc-manganese dioxide (i.e., alkaline) batteries.2,3 2.3.3 Rechargeable Alkaline Batteries Like zinc-carbon batteries, alkaline batteries are not generally rechargeable. One major battery manufacturer, however, has designed a “reusable alkaline” battery that they market as being rechargeable “25 times or more.”4 This manufacturer states that its batteries do not suffer from memory effects as the Ni-Cd batteries do, and that their batteries have a shelf life that is much longer than Ni-Cd batteries—almost as long as the shelf life of primary alkaline batteries.

Also, the manufacturer states that their rechargeable alkaline batteries contain no toxic metals, such as mercury or cadmium, to contribute to the poisoning of the environment.

Rechargeable alkaline batteries are most appropriate for low- and moderate-power portable equipment, such as hand-held toys and radio receivers.

2

The Story of Packaged Power, Duracell International, Inc., July, 1995.

3

Certain commercial companies, equipment, instruments, and materials are identified in this report to specify adequately the technical aspects of the reported results. In no case does such identification imply recommendation or endorsement by the National Institute of Justice, or any other U.S. Government department or agency, nor does it imply that the material or equipment identified is necessarily the best available for the purpose.

4

Household Batteries and the Environment, Rayovac Corporation, 1995.

2.3.4 Nickel-Cadmium (Ni-Cd) Nickel-cadmium cells are the most commonly used rechargeable household batteries. They are useful for powering small appliances, such as garden tools and cellular phones. The basic galvanic cell in a Ni-Cd battery contains a cadmium anode, a nickel hydroxide cathode, and an alkaline electrolyte. Equation 3 shows the chemical reaction in a Ni-Cd cell. Batteries made from Ni-Cd cells offer high currents at relatively constant voltage and they are tolerant of physical abuse. Nickel-cadmium batteries are also tolerant of inefficient usage cycling. If a Ni-Cd battery has incurred memory loss (Sec. 3.4), a few cycles of discharge and recharge can often restore the battery to nearly “full” memory.

Cd 2H2O 2NiOOH 2Ni(OH)2 Cd(OH)2 Equation 3. The chemical reaction in a nickel-cadmium battery.

Unfortunately, nickel-cadmium technology is relatively expensive. Cadmium is an expensive metal and is toxic. Recent regulations limiting the disposal of waste cadmium (from cell manufacturing or from disposal of used batteries) has contributed to the higher costs of making and using these batteries.

These increased costs do have one unexpected advantage. It is more cost effective to recycle and reuse many of the components of a Ni-Cd battery than it is to recycle components of other types of batteries. Several of the major battery manufacturers are leaders in such recycling efforts.

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New Technology Batteries Guide

2.3.5 Nickel-Metal Hydride (Ni-MH) Battery designers have investigated several other types of metals that could be used instead of cadmium to create high-energy secondary batteries that are compact and inexpensive. The nickel-metal-hydride cell is a widely used alternative.

The anode of a Ni-MH cell is made of a hydrogen storage metal alloy, the cathode is made of nickel oxide, and the electrolyte is a potassium hydroxide solution.

2.3.7 Nickel-Zinc (Ni-Z) Another alternative to using cadmium electrodes is using zinc electrodes. Although the nickel-zinc cell yields promising energy output, the cell has some unfortunate performance limitations that prevent the cell from having a useful lifetime of more than 200 or so charging cycles. When nickel-zinc cells are recharged, the zinc does not redeposit in the same â&#x20AC;&#x153;holesâ&#x20AC;? on the anode that were created during discharge. Instead, the zinc redeposits in a somewhat random fashion, causing the electrode to become misshapen.

Over time, this leads to the physical weakening and eventual failure of the electrode.

According to one manufacturer, Ni-MH cells can last 40% longer than the same size Ni-Cd cells and will have a life-span of up to 600 cycles.5 This makes them useful for highenergy devices such as laptop computers, cellular Lithium will ignite or explode phones, and camcorders. contact with water.

Ni-MH batteries have a high self-discharge rate and are relatively expensive.

2.3.6 Nickel-Iron (Ni-I) Nickel-iron cells, also known as the Edison battery, are much less expensive to build and to dispose of than nickel-cadmium cells.

Nickel-iron cells were developed even before the nickel-cadmium cells. The cells are rugged and reliable, but do not recharge very efficiently. They are widely used in industrial settings and in eastern Europe, where iron and nickel are readily available and inexpensive.

5

The Story of Packaged Power, Duracell International, Inc., July, 1995.

10

Lithium and Lithium Ion Lithium is a on promising reactant in battery technology, due to its high electropositivity. The specific energy of some lithium-based cells can be five times greater than an equivalent-sized lead-acid cell and three times greater than alkaline batteries.6 Lithium cells will often have a starting voltage of 3.0 V. These characteristics translate into batteries that are lighter in weight, have lower per-use costs, and have higher and more stable voltage profiles. Equation 4 shows the chemical reaction in one kind of lithium cell.

6

2.3.8

Why Use Energizer AA Lithium Batteries?, Eveready Battery Company, Inc., 1993.

New Technology Batteries Guide

Li MnO2 LiMnO2 Equation 4. The chemical reaction in a lithium-manganese dioxide cell.

Unfortunately, the same feature that makes lithium attractive for use in batteries—its high electrochemical potential—also can cause serious difficulties in the manufacture and use of such batteries. Many of the inorganic components of the battery and its casing are destroyed by the lithium ions and, on contact with water, lithium will react to create hydrogen which can ignite or can create excess pressure in the cell. Many fire extinguishers are water based and will cause disastrous results if used on lithium products.

Special D-class fire extinguishers must be used when lithium is known to be within the boundaries of a fire.7 Lithium also has a relatively low melting temperature for a metal, 180 (C (356 (F). If the lithium melts, it may come into direct contact with the cathode, causing violent chemical reactions.

Because of the potentially violent nature of lithium, the Department of Transportation (DOT) has special guidelines for the transport and handling of lithium batteries. Contact them to ask for DOT Regulations 49 CFR. Some manufacturers are having success with lithium-iron sulfide, lithium-manganese dioxide, lithium-carbon monoflouride, lithium-cobalt oxide, and lithium-thionyl cells.

7

Battery Engineering Web Site, http://www.batteryeng.com/, August 1997.

In recognition of the potential hazards of lithium components, manufacturers of lithiumbased batteries have taken significant steps to add safety features to the batteries to ensure their safe use.

Lithium primary batteries (in small sizes, for safety reasons) are currently being marketed for use in flash cameras and computer memory. Lithium batteries can last three times longer than alkaline batteries of the same size.8 But, since the cost of lithium batteries can be three times that of alkaline batteries, the cost benefits of using lithium batteries are marginal.

Button-size lithium batteries are becoming popular for use in computer memory back-up, in calculators, and in watches. In applications such as these, where changing the battery is difficult, the longer lifetime of the lithium battery makes it a desirable choice.

One company now produces secondary lithium-ion batteries with a voltage of 3.7 V, “four times the energy density of Ni-Cd batteries,” “one-fifth the weight of Ni-Cd batteries,” and can be recharged 500 times.9 In general, secondary (rechargeable) lithiumion batteries have a good high-power performance, an excellent shelf life, and a better life span than Ni-Cd batteries.

Unfortunately, they have a very high initial

8

Navy Primary and Secondary Batteries.

Design and Manufacturing Guidelines, NAVSO P3676, September 1991.

9

Battery Engineering Web Site, http://www.batteryeng.com/, August 1997.

11

New Technology Batteries Guide

cost and the total energy available per usage cycle is somewhat less than Ni-Cd batteries.

2.4 SPECIALTY BATTERIES (“BUTTON” AND MINIATURE BATTERIES) “Button” batteries are the nickname given to the category of batteries that are small and shaped like a coin or a button. They are typically used for small devices such as cameras, calculators, and electronic watches.

Miniature batteries are very small batteries that can be custom built for devices, such as hearing aids and electronic “bugs,” where even button batteries can be too large. Industry standardization has resulted in five to ten standard types of miniature batteries that are used throughout the hearing-aid industry.

Together, button batteries and miniature batteries are referred to as specialty batteries.

Most button and miniature batteries need a very high energy density to compensate for their small size. The high energy density is achieved by the use of highly electropositive—and expensive—metals such as silver or mercury. These metals are not cost effective enough to be used in larger batteries.

Several compositions of specialty batteries are described in the following sections.

2.4.1 Metal-Air Cells A very practical way to obtain high energy density in a galvanic cell is to utilize the oxygen in air as a “liquid” cathode. A metal, such as zinc or aluminum, is used as the anode. The oxygen cathode is reduced in a portion of the cell that is physically isolated from the anode. By using a gaseous cathode, 12

more room is available for the anode and electrolyte, so the cell size can be very small while providing good energy output. Small metal-air cells are available for applications such as hearing aids, watches, and clandestine listening devices.

Metal-air cells have some technical drawbacks, however. It is difficult to build and maintain a cell where the oxygen acting as the cathode is completely isolated from the anode.

Also, since the electrolyte is in direct contact with air, approximately one to three months after it is activated, the electrolyte will become too dry to allow the chemical reaction to continue. To prevent premature drying of the cells, a seal is installed on each cell at the time of manufacture. This seal must be removed by the customer prior to first use of the cell.

Alternately, the manufacturer can provide the battery in an air-tight package.

2.4.2 Silver Oxide Silver oxide cells use silver oxide as the cathode, zinc as the anode, and potassium hydroxide as the electrolyte. Silver oxide cells have a moderately high energy density and a relatively flat voltage profile. As a result, they can be readily used to create specialty batteries. Silver oxide cells can provide higher currents for longer periods than most other specialty batteries, such as those designed from metal-air technology. Due to the high cost of silver, silver oxide technology is currently limited to use in specialty batteries.

2.4.3 Mercury Oxide Mercury oxide cells are constructed with a zinc anode, a mercury oxide cathode, and potassium hydroxide or sodium hydroxide as the electrolyte. Mercury oxide cells have a

New Technology Batteries Guide

high energy density and flat voltage profile resembling the energy density and voltage profile of silver oxide cells. These mercury oxide cells are also ideal for producing specialty batteries. The component, mercury, unfortunately, is relatively expensive and its disposal creates environmental problems.

2.5 OTHER BATTERIES This section describes battery technology that is not mature enough to be available off-theshelf, has special usage limitations, or is otherwise impractical for general use.

2.5.1 Nickel-Hydrogen (Ni-H) Nickel-hydrogen cells were developed for the U.S. space program. Under certain pressures and temperatures, hydrogen (which is, surprisingly, classified as an alkali metal) can be used as an active electrode opposite nickel.

Although these cells use an environmentally attractive technology, the relatively narrow range of conditions under which they can be used, combined with the unfortunate volatility of hydrogen, limits the long-range prospects of these cells for terrestrial uses.

2.5.2 Thermal Batteries A thermal battery is a high-temperature, molten-salt primary battery. At ambient temperatures, the electrolyte is a solid, nonconducting inorganic salt. When power is required from the battery, an internal pyrotechnic heat source is ignited to melt the solid electrolyte, thus allowing electricity to be generated electrochemically for periods from a few seconds to an hour. Thermal batteries are completely inert until the electrolyte is melted and, therefore, have an excellent shelf life, require no maintenance, and can tolerate

physical abuse (such as vibrations or shocks) between uses.

Thermal batteries can generate voltages of 1.5 V to 3.3 V, depending on the batteryâ&#x20AC;&#x2122;s composition. Due to their rugged construction and absence of maintenance requirements, they are most often used for military applications such as missiles, torpedoes, and space missions and for emergency-power situations such as those in aircraft or submarines.

The high operating temperatures and short active lives of thermal batteries limit their use to military and other large-institution applications.

2.5.3 Super Capacitor This kind of battery uses no chemical reaction at all. Instead, a special kind of carbon (carbon aerogel), with a large molecular surface area, is used to create a capacitor that can hold a large amount of electrostatic energy.10 This energy can be released very quickly, providing a specific energy of up to 4000 Watt-hours per kilogram (Wh/kg), or it can be regulated to provide smaller currents typical of many commercial devices such as flashlights, radios, and toys. Because there are no chemical reactions, the battery can be recharged hundreds of thousands of times without degradation. Other potential advantages of this kind of cell are its low cost and wide temperature range. One disadvantage, however, is its high self-discharge rate. The voltage of some prototypes is approximately 2.5 V.

10

PolyStor Web Page, http://www.polystor.com/, August, 1997.

13

New Technology Batteries Guide

2.5.4 The Potato Battery One interesting science experiment involves sticking finger-length pieces of copper and zinc wire, one at a time, into a raw potato to create a battery. The wires will carry a very weak current which can be used to power a small electrical device such as a digital clock.

One vendor sells a novelty digital watch that is powered by a potato battery. The wearer must put a fresh slice of potato in the watch every few days.

2.5.5 The Sea Battery Another interesting battery design uses a rigid framework, containing the anode and cathode, which is immersed into the ocean to use sea water as the electrolyte. This configuration seems promising as an emergency battery for marine use.

2.5.6 Other Developments Scientists are continually working on new combinations of materials for use in batteries, as well as new manufacturing methods to extract more energy from existing configurations.

14

3. Performance, Economics and Tradeoffs 3.1 ENERGY DENSITIES The energy density of a battery is a measure of how much energy the battery can supply relative to its weight or volume. A battery with an energy density twice that of another battery should, theoretically, have an active lifetime twice as long.

The energy density of a battery is mainly dependent on the composition of its active components. A chemist can use mathematical equations to determine the theoretical maximum voltage and current of a proposed cell, if the chemical composition of the anode, cathode, and electrolyte of the cell are all known. Various physical attributes, such as purity of the reactants and the particulars of the manufacturing process can cause the measured voltage, current, and capacity to be lower than their theoretical values.

3.2 ENERGY

Figure 2. Energy densities, W#h/kg, of various battery types (adapted from NAVSO P-3676).

3.3 ENERGY PER VOLUME Figure 3 compares the volumetric energy densities of various dry cell systems discharged at a constant rate for temperatures between -40 (C (-40 (F) and 60 (C (140 (F).

PER MASS

Figure 2 compares the gravimetric energy densities of various dry cell systems discharged at a constant rate for temperatures between -40 (C (-40 (F) and 60 (C (140 (F).

Of the systems shown, the zinc-air cell produces the highest gravimetric energy density. Basic zinc-carbon cells have the lowest gravimetric energy density.

Of the systems shown, the zinc-air cell produces the highest volumetric energy density. Basic zinc-carbon cells have the lowest volumetric energy density. The curves for secondary battery cells are not shown in the tables.

15

New Technology Batteries Guide

much energy is needed for a repeated application.

The physical process that causes the memory effect is the formation of potassium-hydroxide crystals inside the cells. This build up of crystals interferes with the chemical process of generating electrons during the next batteryuse cycle. These crystals can form as a result of repeated partial discharge or as a result of overcharging the Ni-Cd battery.

Figure 3. Energy densities, W#h/L, of various battery types (adapted from NAVSO P-3676).

Of the major types of secondary cells, Ni-Cd batteries and wet-cell lead-acid batteries have approximately the same volumetric energy density. Ni-MH batteries have approximately twice the volumetric energy density of Ni-Cd batteries.

3.4 MEMORY EFFECTS As a rechargeable battery is used, recharged, and used again, it loses a small amount of its overall capacity. This loss is to be expected in all secondary batteries as the active components become irreversibly consumed.

Ni-Cd batteries, however, suffer an additional problem, called the memory effect. If a Ni-Cd battery is only partially discharged before recharging it, and this happens several times in a row, the amount of energy available for the next cycle will only be slightly greater than the amount of energy discharged in the cellâ&#x20AC;&#x2122;s most-recent cycle. This characteristic makes it appear as if the battery is â&#x20AC;&#x153;rememberingâ&#x20AC;? how

16

The build up of potassium-hydroxide crystals can be reduced by periodically reconditioning the battery. Reconditioning of a Ni-Cd battery is accomplished by carefully controlled power cycling (i.e., deeply discharging and then recharging the battery several times). This power cycling will cause most of the crystals to redissolve back into the electrolyte. Several companies offer this reconditioning service, although battery users can purchase a reconditioner and recondition their own batteries. Some batteries can be reconditioned without a special reconditioner by completely draining the battery (using the battery powered device itself or a resistive circuit designed to safely discharge the battery) and charging it as normal.

3.5 VOLTAGE PROFILES The voltage profile of a battery is the relationship of its voltage to the length of time it has been discharging (or charging). In most primary batteries, the voltage will drop steadily as the chemical reactions in the cell are diminished. This diminution leads to an almost-linear drop in voltage, called a sloping profile. Batteries with sloping voltage profiles provide power that is adequate for many

New Technology Batteries Guide

applications such as flashlights, flash cameras, and portable radios.

Ni-Cd batteries provide a relatively flat voltage profile. The cellâ&#x20AC;&#x2122;s voltage will remain relatively constant for more than E of its discharge cycle. At some point near the end of the cycle, the voltage drops sharply to nearly zero volts. Batteries with this kind of profile are used for devices that require a relatively steady operating voltage.

One disadvantage of using batteries with a flat voltage profile is that the batteries will need to be replaced almost immediately after a drop in voltage is noticed. If they are not immediately replaced, the batteries will quickly cease to provide any useful energy.

Figure 4 shows the conceptual difference between a flat discharge rate and a sloping discharge rate.

3.6 SELF-DISCHARGE RATES All charged batteries (except thermal batteries and other batteries specifically designed for a near-infinite shelf life) will slowly lose their charge over time, even if they are not connected to a device. Moisture in the air and the slight conductivity of the battery housing will serve as a path for electrons to travel to the cathode, discharging the battery. The rate at which a battery loses power in this way is called the self-discharge rate.

Ni-Cd batteries have a self-discharge rate of approximately 1% per day. Ni-MH batteries have a much higher self-discharge rate of approximately 2% to 3% per day. These high discharge rates require that any such battery, which has been stored for more than a month, be charged before use.

Primary and secondary alkaline batteries have a self-discharge rate of approximately 5% to 10% per year, meaning that such batteries can have a useful shelf life of several years.

Lithium batteries have a self-discharge rate of approximately 5% per month.

3.7 OPERATING TEMPERATURES

Figure 4. Flat discharge curve vs. sloping discharge curve.

Figure 5 (Sec. 5) shows actual voltage profiles for several common battery types.

As a general rule, battery performance deteriorates gradually with a rise in temperature above 25 (C (77 (F), and performance deteriorates rapidly at temperatures above 55 (C (131 (F). At very low temperatures -20 (C (-4 (F) to 0 (C (32 (F), battery performance is only a fraction of that at 25 (C (77 (F). Figure 2 and Figure 3 show the differences in energy density as a function of temperature.

At low temperatures, the loss of energy capacity is due to the reduced rate of chemical 17

New Technology Batteries Guide

reactions and the increased internal resistance of the electrolyte. At high temperatures, the loss of energy capacity is due to the increase of unwanted, parasitic chemical reactions in the electrolyte.

Ni-Cd batteries have a recommended temperature range of +17 (C (62 (F) to 37 (C (98 (F). Ni-MH have a recommended temperature range of 0 (C (32 (F) to 32 (C (89 (F).

3.8 CYCLE LIFE The cycle life of a battery is the number of discharge/recharge cycles the battery can sustain, with normal care and usage patterns, before it can no longer hold a useful amount of charge.

Ni-Cd batteries should have a normal cycle life of 600 to 900 recharge cycles. Ni-MH batteries will have a cycle life of only 300 to 400 recharge cycles. As with all rechargeable batteries, overcharging a Ni-Cd or Ni-MH battery will significantly reduce the number of cycles it can sustain.

predetermined level of discharge. This kind of test simulates the battery usage of a portable radio.

A comparison of these two kinds of tests was performed on five commonly available types of batteries.11 The data shows that the five tested batteries all had a constant-load duration of 60 to 80 minutes, which indicates that the five batteries had similar capacities.

But, intermittent-load testing of those same five batteries showed that the duration of the batteries ranged from 8.5 hours to 12 hours.

There was no correlation of the results of the two tests, meaning that batteries that performed best under constant-load testing did not necessarily perform well under intermittent-load testing. The study concluded that the ability of a battery to recover itself between heavy current drains cannot be made apparent through a constant-load test.

3.10 BATTERY TECHNOLOGY COMPARISON Table 3 shows a comparison of some of the performance factors of several common battery types.

3.9 CAPACITY TESTING Many battery manufacturers recommend the constant-load test to determine the capacity of a battery. This test is conducted by connecting a predetermined load to the battery and then recording the amount of time needed to discharge the battery to a predetermined level.

Another recommended test is the intermittentor switching-load test. In this type of test, a predetermined load is applied to the battery for a specified period and then removed for another period. This load application and removal is repeated until the battery reaches a 18

The initial capacity of a battery refers to the electrical output, expressed in ampere-hours, which the fresh, fully charged battery can deliver to a specified load. The rated capacity is a designation of the total electrical output of the battery at typical discharge rates; e.g., for each minute of radio transceiver operation, 6 seconds shall be under a transmit current

11

Batteries Used with Law Enforcement Communications Equipment: Chargers and Charging Techniques, W. W. Scott, Jr., U.S. Department of Justice, LESP-RPT-0202.00, June 1973.

New Technology Batteries Guide

drain, 6 seconds shall be under a receive current drain and 48 seconds shall be under a standby current drain.

The self-discharge rate is the rate at which the battery will lose its charge during storage or other periods of non-use. The cycle life is the number of times that the rechargeable battery can be charged and discharged before it becomes no longer able to hold or deliver any useful amount of energy.

The initial cost is the relative cost of purchasing the battery. The life-cycle cost is the per-use relative cost of the battery.

Table 4 shows a more detailed comparison of many of the available battery types.

Table 3. Battery Technology Comparison (adapted from Design Note: Renewable Reusable Alkaline Batteries) (See Sec. 3.10)

Ni-Cd

Ni-MH

|| NNNN Rated Capacity qqq || Self-Discharge r NNNN Cycle Life NNNN r Initial Cost* r NNNN Life-Cycle Cost* qqq r Worst Performance = r, Low Performance = ||, Good Performance= qqq, Best Performance =NNNN Initial Capacity

r NNNN || NNNN || qqq

Primary Alkaline

Secondary Alkaline

qqq r NNNN qqq qqq qqq

*A better performance ranking means lower costs.

19

Cell Type*

Basic Type**

Anode material

Cathode Material

Main Electrolyte Material

Volts per Cell

Carbon-Zinc (“Leclanché”)

P

Zinc

Manganese dioxide

Ammonium chloride, zinc chloride

Zinc Chloride

P

Zinc

Manganese dioxide

“Alkaline” (ZincManganese Dioxide)

P or S

Zinc

Car Battery (Lead-Acid)

S

Lead

Advantages & Applications

Disadvantages

1.5

Low cost, good shelf life. Useful for flashlights, toys, and small appliances.

Output capacity decreases as it drains; poor performance at low temperatures.

Zinc Chloride

1.5

Good service at high drain, leak resistant, good low-temperature performance. Useful for flashlights, toys, and small appliances.

Relatively expensive for novelty usage.

Manganese dioxide

Potassium hydroxide

1.5

High efficiency under moderate, continuous drains, long shelf life, good low-temperature performance. Useful for camera flash units, motor-driven devices, portable radios.

Primary cells are expensive for novelty usage.

Secondary cells have a limited number of recharge cycles.

Lead dioxide

Sulfuric acid

2

Low cost, spill resistant (sealed batteries). Useful for automobiles and cordless electric lawn mowers.

Limited lowtemperature performance.

Vented cells require maintenance.

Cells are relatively heavy.

* -- Common name, ** -- P=Primary, S=Secondary (Rechargeable)

New Technology Batteries Guide

20

Table 4. A Comparison of Several Popular Battery Types

Table 4 (continued) Cell Type*

Basic Type**

Anode material

Cathode Material

Main Electrolyte Material

Volts per Cell

Advantages & Applications

â&#x20AC;&#x153;Ni-Cdâ&#x20AC;? (NickelCadmium)

S

Cadmium

Nickel hydroxide

Potassium hydroxide

1.25

Excellent cycle life; flat discharge curve; good high- and lowtemperature performance; high resistance to shock and vibration. Useful for small appliances that have intermittent usage, such as walkie-talkies, portable hand tools, tape players, and toys. When batteries are exhausted, they can be recharged before the next needed use.

High initial cost; only fair charge retention; memory effect.

Mercuric Oxide

P

Zinc

Mercuric oxide

Potassium hydroxide

1.35

Relatively flat discharge curve; relatively high energy density; good high-temperature performance; good service maintenance.

Useful for critical appliances, such as paging, hearing aids, and test equipment.

Poor lowtemperature performance in some situations.

21

New Technology Batteries Guide

* -- Common name, ** -- P=Primary, S=Secondary (Rechargeable)

Disadvantages

Cell Type*

Basic Type**

Anode material

Cathode Material

Main Electrolyte Material

Volts per Cell

Advantages & Applications

â&#x20AC;&#x153;Ni-MHâ&#x20AC;?

(Nickel-Metal Hydride)

S

Hydrogen storage metal

Nickel oxide

Potassium hydroxide

1.5

No memory effects (such as Ni-Cd has), good high-power performance, good lowtemperature performance. Useful for portable devices where the duty cycle varies from use to use.

High initial cost, relatively high rate of selfdischarge.

Silver Oxide

P or S

Zinc

Silver oxide

Potassium hydroxide

1.5

High energy density; flat discharge curve. Useful for very small appliances such as calculators, watches, and hearing aids.

Silver is very expensive; poor storage and maintenance characteristics.

Rechargeable cells have a very limited number of cycles.

Zinc-Air

P

Zinc

Oxygen

Potassium hydroxide

1.25

High energy density in small cells. Flat discharge rate.

Dries out quickly.

Lithium

P

Lithium

Iron sulfide

Lithium salts in ether

1.0 3.6

Good energy density.

Limited high-rate capacities; safety concerns.

* -- Common name, ** -- P=Primary, S=Secondary (Rechargeable)

Disadvantages

New Technology Batteries Guide

22

Table 4 (continued)

4. Selecting the Right Battery for the Application Batteries come in many different shapes, sizes, and compositions. There is no one â&#x20AC;&#x153;idealâ&#x20AC;? battery that can satisfy all possible requirements equally. Different battery technologies have been developed that will optimize certain parameters for specific battery uses.

However, the small differences that do exist between batteries made by different manufacturers, can be significant when using a multi-cell array of matched cells. In these cases, potential replacement cells must be graded to see if the cells properly match the capacity of the existing cells.

In general, the Even for nonenergy output matched, multiof a battery is cell related only to applications, its size and such as material flashlights, composition. portable radios, Different etc., it is still a battery designs good rule of and different thumb to avoid manufacturing mixing batteries methods (for from different the same type, manufacturers size, and within one composition of device. Small battery) will, in Figure 5. Performance comparison of primary and variances in general, lead to secondary alkaline and Ni-Cd batteries (adapted from voltage and only minor current, Design Note: Renewable Reusable Alkaline Batteries). differences in between the batteriesâ&#x20AC;&#x2122; electrical output. Batterydifferent brands of battery, can slightly shorten industry standards have contributed to the fact the useful life span of all of the batteries. that batteries (of the same type, composition, and size) from different manufacturers are Do not mix batteries of different types (e.g., quite interchangeable. do not mix rechargeable alkaline batteries with Ni-Cd batteries) within a single device or within an array of batteries.

23

New Technology Batteries Guide

Figure 5 shows some discharge curves for several popular AA size battery types. Two of the curves (secondary alkaline [1st use] and [25th use]) show that secondary alkaline batteries rapidly lose their capacity as they are used and recharged. Only one Ni-Cd curve is shown, since its curve remains essentially the same throughout most its life span.

4.1 BATTERY PROPERTIES Battery applications vary, as do considerations for selecting the correct battery for each application. Some of the important factors that customers might consider when selecting the right battery for a particular application are listed below: Chemistry -- Which kind of battery chemistry is best for the application?

Different chemistries will generate different voltages and currents.

Primary or Secondary -- Primary batteries are most appropriate for applications where infrequent, high-energy output is required. Secondary batteries are most appropriate for use in devices that see steady periods of use and non-use (pagers, cellular phones, etc.).

Standardization and Availability -- Is there an existing battery design that meets the application needs? Will replacement batteries be available in the future? Using existing battery types is almost always preferable to specifying a custom-made battery design.

Flexibility -- Can the battery provide high or low currents over a wide range of conditions?

Temperature Range -- Can the battery provide adequate power over the 24

expected temperature range for the application?

Good Cycle Life -- How many times can the rechargeable battery be discharged and recharged before it becomes unusable?

Costs -- How expensive is the battery to purchase? Does the battery require special handling?

Shelf Life -- How long can the battery be stored without loss of a significant amount of its power?

Voltage -- What is the voltage of the battery? [Most galvanic cells produce voltages of between 1.0 and 2.0 V.] Safety -- Battery components range from inert, to mildly corrosive, to highly toxic or flammable. The more hazardous components will require additional safety procedures.

Hidden Costs -- Simpler manufacturing processes result in lower cost batteries. However, if a battery contains toxic or hazardous components, extra costs will be incurred to dispose of the battery safely after its use.

Table 5 shows a short list of different battery types and the kinds of application that are appropriate for each.

4.2 ENVIRONMENTAL CONCERNS All battery components, when discarded, contribute to the pollution of the environment.

Some of the components, such as paperboard and carbon powder, are relatively organic and can quickly merge into the ecosystem without noticeable impact. Other components, such as steel, nickel, and plastics, while not actively

New Technology Batteries Guide

toxic to the ecosystem, will add to the volume of a landfill, since they decompose slowly.

Table 5. Recommended Battery Types for Various Usage Conditions Battery Type

Device Drain Rate

Device Use Frequency

Primary Alkaline

High

Moderate

Secondary Alkaline

Moderate

Moderate

Primary Lithium

High

Frequent

Secondary Ni-Cd

High

Frequent

Primary Zn-C (“Heavy Duty”)

Moderate

Regular

Primary Zn-C (“Standard”)

Low

Occasional

1980, to 0.00%, in 1996.12 Other manufacturers report that their current battery formulas contain no mercury. The U.S. Department of Mines, in 1994, estimated that, for the U.S. production of household batteries, mercury usage had fallen from 778 tons in 1984 to (a projected) 10 tons in 1995.13 Many of the major battery manufacturers have put significant efforts into the recycling of discarded batteries. According to one manufacturer, it takes six to ten times more energy to recycle a battery than to create the battery components from virgin materials.

Efforts are underway that could improve the recycling technology to make recycling batteries much more energy efficient and cost effective.14 The use of secondary (rechargeable) batteries is more cost efficient than the use of primary batteries. Such use will reduce the physical volume of discarded batteries in landfills, because the batteries can be recharged and reused 25 to 1000 times before they must be discarded.

Of most concern, however, are the heavy-metal battery Many of the major battery manufacturers components, have put significant efforts into the which, when recycling of discarded batteries. discarded, can be toxic to plants, animals, and humans. Cadmium, lead, and mercury are the heavy-metal components most likely to be the target of environmental concerns.

12 Eveready and the Environment, Eveready Battery Company, Inc., 1995.

Several of the major battery manufacturers have taken steps to reduce the amount of toxic materials in their batteries. One manufacturer reports the reduction of the mercury content of their most-popular battery from 0.75%, in

13

Eveready and the Environment, Eveready Battery Company, Inc., 1995.

14

Eveready and the Environment, Eveready Battery Company, Inc., 1995.

25

New Technology Batteries Guide

The most popular secondary batteries, however, contain cadmium. Many manufacturers, responding to customer requests and legislative demands, are designing nickel-metal hydride, lithium-ion, and rechargeable-alkaline secondary batteries that contain only trace amounts of cadmium, lead, or mercury.

4.3 STANDARDIZATION Existing off-the-shelf batteries are often preferred to batteries that require special design and manufacturing. Some benefits of using off-the-shelf batteries are listed below: The use of a proven design can reduce the risk of the battery not working properly.

The use of tested technology eliminates costly and time-consuming development efforts.

Standard duty cycles for battery service life and capacity determinations are defined in EIA/TIA Standard 60315 for land mobile radio communications and NIJ Standard-0211.0116 for hand-held portable radio applications.

Specifically, in an average 1 minute period of mobile-radio usage, 6 seconds (10%) is spent receiving, 6 seconds (10%) is spent transmitting and 48 seconds (80%) is spent in the idle mode. Table 8 provides an example of a transceiver drawing an average current of 8.0 + 6.2 + 32.5 = 46.7 mA. For a typical duty cycle composed of 8 hours of operation (followed by 16 hours of rest) a minimum battery capacity of 374 mAh is required. One manufacturer of portable communications equipment recommends that batteries be replaced if they fail to deliver 80% or more of their original rated capacity. Below 80% batteries are usually found to deterioriate quickly. Because a minimum requirement of 374 mAh is 75% of the rated capacity of a 500 mAh battery, the latter should adequately provide power for the entire duty described.17

The use of a proven design reduces unit production costs because of competitive, multi-source availability.

The use of tested technology reduces operations and support costs through commonality of training, documentation, and replacement efforts.

4.4 TESTING CAPACITIES One method of estimating battery capacity requirements for a specific battery-powered device is to calculate the current drawn during the typical duty cycle for the device.

15

Land Mobile FM or PM Communications Equipment, Measurement and Performance Standard, Electronics Industry Association/Telecommunications Industry Association, Publication EIA/TIA 603, 1993.

16

Rechargeable Batteries for Personal/ Portable Transceivers, National Institute of Justice, NIJ Standard-0211.01, 1995.

17

Batteries Used with Law Enforcement Communications Equipment: Chargers and Charging Techniques, W.W. Scott, Jr., National Institute of Justice, LESP-RPT-0202.00, June 1973.

26

New Technology Batteries Guide

Table 6. Typical Usage of Portable Telecommunications Equipment.

Standby Mode

Receive Mode

Transmit Mode

80% (48 minutes of each hour)

10% (6 minutes of each hour)

10% (6 minutes of each hour)

Current Drain for Mode

10 mA

62 mA

325 mA

Average Current for Mode

8.0 mA

Percent of Duty Cycle

6.2 mA

32.5 mA

Similar calculations can be performed for any battery in any battery-powered device by using the data relevant to the device and the proposed battery. The manufacturers should either provide such appropriate information with the batteries and devices, or they should be able to provide those data on request.

4.5 MOBILE RADIOS As reported above, mobile radios have a typical duty cycle of 10% transmit, 10% receive, and 80% standby. The maximum current drain will occur during the transmit cycle. Each radio, typically, will have a daily cycle of 8 hours of use and 16 hours of nonuse. The non-use hours may be used to charge the radioâ&#x20AC;&#x2122;s batteries.

Most commercial, off-the-shelf mobile-radio units include a battery. But, since many radio units are in service 7 days a week, 52 weeks a year, and since the batteries are discharged and recharged daily, each set of batteries should wear out approximately once every two years (~700 recharge cycles). Replacement batteries

should be purchased as directed by the user manual for the unit.

4.6 CELLULAR PHONES AND PCS PHONES Most commercial, off-the-shelf cellular phones contain a battery when purchased.

Charging units may be supplied with the phone or may be purchased separately.

Typical usage for cellular telephones will vary significantly with user, but, the estimate for mobile radio usage (10% of the duty cycle is spent in transmit mode, 10% in receive mode, and 80% in standby mode) is also a reasonable estimate for cellular phone usage. At the end of each usage cycle, the user places the battery (phone) on a recharging unit that will charge the battery for the next usage cycle. This usage pattern is appropriate for Ni-Cd or Ni-MH batteries. Ni-Cd batteries should be completely discharged between uses to prevent memory effects created by a recurring duty cycle.

When a replacement or spare battery is needed, only replacements, recommended by the phone manufacturer should be used.

Batteries and battery systems from other manufacturers may be used if the batteries are certified to work with that particular brand and model of phone. Damage to the phone may result if non-certified batteries are used.

Several battery manufacturers make replacement battery packs that are designed to work with a wide variety of cellular phones.

Because of the variety of phones available, battery manufacturers must design and sell several dozen different types of batteries to fit the hundreds of models of cellular phones 27

New Technology Batteries Guide

from dozens of different manufacturers.18 The user is advised to check battery interoperability charts before purchasing a replacement battery.

One battery manufacturer offers a battery replacement system that allows a phone owner to use household primary batteries, inserted into a special housing (called a refillable battery pack), to replace the phone’s regular rechargeable battery pack. This refillable pack, says the manufacturer, is designed for lightuse customers, who require that their phone’s batteries have the long shelf life of primary batteries. This refillable pack can also be used in emergencies, for example, where the phone’s rechargeable battery pack is exhausted and no recharged packs are available. Primary household batteries can be readily purchased (or borrowed from other devices), inserted into the refillable pack, and used to power the phone.19

and at the self-discharge rate when the computer is shut off. Quite often, the user will use the computer until the “low battery” alarm sounds. At this point, the battery will be drained of 90% of its charge before the user recharges it. The computer will also register regular periods of non-use, during which the battery can be recharged. Secondary Ni-Cd batteries are most appropriate for this usage pattern.

When a laptop-computer battery reaches the end of its life cycle, it should be replaced with a battery designed specifically for that laptop computer. Using other types of batteries may damage the computer. The user’s manual for the laptop computer will list one or more battery types and brands that may be used. If in doubt, the user is advised to contact the manufacturer of the laptop computer and ask for a battery-replacement recommendation.

4.8 CAMCORDERS

4.7 LAPTOP COMPUTERS Most commercial, off-the-shelf laptop computers have a built-in battery system. In addition to the battery provided, most laptops will have a battery adapter that also serves as a battery charger.

The expected usage of a laptop computer is that the operator will use it several times a week, for periods of several hours at a time.

The computer will drain the battery at a moderate rate when the computer is running,

18

Easy to Choose, Easy to Use, Eveready Battery Corporation, 1997.

19

Cellular Duracell Rechargeable Batteries, Duracell, 1996.

28

Almost all commercial, off-the-shelf camcorders come with a battery and a recharging unit when purchased.

The camcorder is typically operated continuously for several minutes or hours (to produce a video recording of some event).

This use will require that the battery provide approximately 2 hours of non-stop recording time. The electric motor driving the recording tape through the camcorder requires a moderately high amount of power throughout the entire recording period.

Rechargeable Ni-Cd or Ni-MH batteries or primary lithium batteries are usually the only choice for camcorder use. Several battery manufacturers produce Ni-Cd or Ni-MH

New Technology Batteries Guide

batteries that are specially designed for use in camcorders. Due to the lack of sufficient standardization for these kind of batteries, the battery manufacturers must design and sell approximately 20 different camcorder batteries to fit at least 100 models of camcorders from over a dozen manufacturers.20 Camcorder batteries are usually designed to provide 2 hours of service, but larger batteries are available that can provide up to 4 hours of service.

Lithium camcorder batteries can provide three to five times the energy of a single cycle of secondary Ni-Cd batteries. These lithium batteries, however, are primary batteries and must be properly disposed of at the end of their life cycle. Secondary lithium-ion camcorder batteries are being developed.

4.9 SUMMARY

_ Alkaline -- The most commonly used primary cell (household) is the zinc-alkaline manganese dioxide battery. They provide more power-per-use than secondary batteries and have an excellent shelf life. _ Rechargeable Alkaline -- Secondary alkaline batteries have a long shelf life and are useful for moderate-power applications. Their cycle life is less than most other secondary batteries. _ Lithium Cells -- Lithium batteries offer performance advantages well beyond the capabilities of conventional aqueous electrolyte battery systems. However, lithium batteries are not widely used because of safety concerns. _ Thermal Batteries -- These are special batteries that are capable of providing very high rates of discharge for short periods of time. They have an extremely long shelf life, but, because of the molten electrolyte and high operating temperature, are impractical for most household uses.

There are six varieties of batteries in use, each with its own advantages and disadvantages.

Below is a short summary of each variety: _ Lead-Acid -- Secondary lead-acid batteries are the most popular worldwide.

Both the battery product and the manufacturing process are proven, economical, and reliable. _ Nickel-Cadmium -- Secondary Ni-Cd batteries are rugged and reliable. They exhibit a high-power capability, a wide operating temperature range, and a long cycle life. They have a self-discharge rate of approximately 1% per day.

20

Camcorder Battery Pocket Guide, Eveready Battery Company, 1996.

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30

5. Battery Handling and Maintenance The following guidelines offer specific advice on battery handling and maintenance. This advice is necessarily not all inclusive. Users are cautioned to observe specific warnings on individual battery labels and to use common sense when handling batteries.

5.1 BATTERY DANGERS 8 To get help, should someone swallow a battery, immediately call The National Battery Ingestion Hot Line collect at (202) 625-3333. Or, call 911 or a state/local Poison Control Center.

8 Batteries made from lead (or other heavy metals) can be very large and heavy and can cause damage to equipment or injuries to personnel if improperly handled.

8 When using lithium batteries, a “Lith-X” or D-Class fire extinguisher should always be available. Water-based extinguishers must not be used on lithium of any kind, since water will react with lithium and release large amounts of explosive hydrogen.

Before abusively testing a battery, contact the manufacturer of the battery to identify any potential dangers.

8 Vented batteries must be properly ventilated. Inadequate ventilation may result in the build up of volatile gases,

which may result in an explosion or asphyxiation.

Do not attempt to solder directly onto a terminal of the battery. Attempting to do so can damage the seal or the safety vent.

When disconnecting a battery from the device it is powering, disconnect one terminal at a time. If possible, first remove the ground strap at its connection with the device’s framework. Observing this sequence can prevent an accidental short circuit and also avoid risking a spark at the battery. In most late-model, domestic automobiles, the battery terminal labeled “negative” is usually connected to the automobile’s framework.

Do not attempt to recharge primary batteries. This kind of battery is not designed to be recharged and may overheat or leak if recharging is attempted.

8 When recharging secondary batteries, use a charging device that is approved for that type of battery. Using an approved charging device can prevent overcharging or overheating the battery. Many chargers have special circuits built into them for correctly charging specific types of batteries and

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will not work properly with other types.

Do not use secondary (rechargeable) batteries in smoke detectors.

Secondary batteries have a high selfdischarge rate. Primary batteries have a much longer shelf life and are much more dependable in emergencies.

Consult the smoke detector’s user manual for the recommended battery types.

Do not attempt to refill or repair a worn-out or damaged battery.

Do not allow direct bodily contact with battery components. Acidic or alkaline electrolyte can cause skin irritation or burns. Electrode materials such as mercury or cadmium are toxic.

Lithium can cause an explosion if it comes into contact with water. Other components can cause a variety of short-term (irritation and burns) or long-term (nerve damage) maladies.

Do not lick a 9 V battery to see if it is charged. You will, of course, be able to determine whether or not the battery is charged, but such a test may result in a burn that may range from simply uncomfortable to serious.

Do not dispose of batteries in a fire. The metallic components of the battery will not burn and the burning electrolyte may splatter, explode, or release toxic fumes. Batteries may be disposed of, however, in industrial incinerators that are approved for the disposal of batteries.

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Do not carry batteries in your pocket.

Coins, keys, or other metal objects can short circuit a battery, which can cause extreme heat, acid leakage, or an explosion.

Do not wear rings, metal jewelry, or metal watchbands while handling charged cells. Severe burns can result from accidentally short circuiting a charged cell. Wearing gloves can reduce this danger.

Do not use uninsulated tools near charged cells. Do not place charged cells on metal workbenches. Severe arcing and overheating can result if the battery’s terminals are shorted by contact with such metal objects.

New Technology Batteries Guide

The Straight Dope

by Cecil Adams, The Chicago Reader Is it true that refrigerating batteries will extend shelf life? If so, why does a cold car battery cause slower starts? The answer will help me sleep better. — Kevin C., Alexandria, Virginia Whatever it takes, dude. Refrigerating batteries extends shelf life because batteries produce electricity through a chemical reaction. Heat speeds up any reaction, while cold slows it down. Freeze your [car battery] and you’ll extend its life because the juice won’t leak away—but it’ll also make those volts a little tough to use right away. That accounts for the belief occasionally voiced by mechanics that if a battery is left on the garage floor for an extended period, the concrete will “suck out the electricity.” It does nothing of the kind, but a cold floor will substantially reduce a battery’s output. The cure: warm it up first.

(Reprinted, with permission, from Return of the Straight Dope. ©1994 Chicago Reader, Inc.)

5.2 EXTENDING BATTERY LIFE 8 Read the instructions for the device before installing batteries. Be sure to orient the battery’s positive and negative terminals correctly when inserting them.

8 To find a replacement battery that works with a given device, call the manufacturer of the device or ask the retailer to check the manufacturer’s battery cross-reference guide.

8 Store batteries in a cool, dark place. This helps extend their shelf life.

Refrigerators are convenient locations.

Although some battery manufacturers say that refrigeration has no positive effect on battery life, they say it has no negative effect either. Do not store batteries in a freezer. Always let batteries come to room temperature before using them.

8 Store batteries in their original boxes or packaging materials. The battery manufacturer has designed the packaging for maximum shelf life.

8 When storing batteries, remove any load or short circuit from their terminals.

8 When storing battery-powered devices for long periods (i.e., more than a month), remove the batteries. This can prevent damage to the device from possible battery leakage. Also, the batteries can be used for other applications while the batteries are still “fresh.”

8 In a device, use only the type of battery that is recommended by the manufacturer of the device.

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8 Use a marking pen to indicate, on the battery casing, the day and year that the battery was purchased. Also, keep track of the number of times the battery has been recharged. Avoid writing on or near the battery terminals.

8 Do not mix batteries from different manufacturers in a multi-cell device (e.g., a flashlight). Small differences in voltage, current, and capacity, between brands, can reduce the average useful life of all the batteries.

8 When using secondary batteries in a multicell device (e.g., a flashlight), try to use batteries of the same age and similar charging histories. This kind of matching will make it more likely that all the batteries will discharge at the same rate, putting less stress on any individual battery.

8 When using single-cell rechargeable Ni-Cd batteries, be sure to discharge the cell completely before recharging it, thus counteracting the “memory” effect.

8 Secondary Ni-Cd batteries can sometimes be reconditioned to reduce the impact of “memory” effects. Completely discharge the battery and recharge it several times.

Do not use batteries in high-temperature situations (unless the battery is designed for that temperature range).

Locate batteries as far away from heat sources as possible. The electrical potential of the battery will degrade rapidly if it is exposed to temperatures 34

higher than those recommended by the manufacturer.

6. Battery Chargers and Adapters of battery, will be able to charge correctly any brand of battery of that same size and type.

6.1 BATTERY CHARGERS Secondary (rechargeable) batteries require a battery charger to bring them back to full power. The charger will provide electricity to the electrodes (opposite to the direction of electron discharge), which will reverse the chemical process within the battery, converting the applied electrical energy into chemical potential energy.

Table 7. Charge Rate Descriptions Description

Do not, however, use a charger designed for one type of battery to charge a different type of battery, even if the sizes are the same. For example, do not use a charger designed for charging “D”-sized Ni-Cd batteries to charge “D”-sized rechargeable alkaline batteries. If in doubt, use only the exact charger recommended by the battery manufacturer.

Charge Rate (Amperes)

Nominal Charge Time (Hours)

Standby (Trickle)

0.01 C to 0.03 C

100 to 33

Slow (Overnight)

0.05 C to 0.1 C

20 to 10

Quick

0.2 C to 0.5 C

5 to 2

Fast

1 C and more

1 and less

Recharging a battery without a recommended charger is dangerous. If too much current is supplied, the battery may overheat, leak, or explode. If not enough current is applied, the battery may never become fully charged, since the self-discharge rate of the battery will nullify the charging effort.

It is not recommended that battery users design and build their own charging units. Many low-cost chargers are available off-the-shelf that do a good job of recharging batteries.

Specific, off-the-shelf chargers are identified and recommended, by each of the major battery manufacturers, for each type of secondary battery they produce.

“C” is the theoretical current needed to completely charge the fully discharged battery in one hour.

Batteries should only be recharged with chargers that are recommended, by the manufacturer, for that particular type of battery. In general, however, battery-industry standards ensure that any off-the-shelf battery charger, specified for one brand, size, and type

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New Technology Batteries Guide

6.2 CHARGE RATES The current that a charger supplies to the battery is normally expressed as a fraction of the theoretical current (for a given battery) needed to charge the battery completely in 1 hour. This theoretical current is called the nominal battery capacity rating and is represented as â&#x20AC;&#x153;C.â&#x20AC;? For example, a current of 0.1 C is that current which, in 10 hours, theoretically, would recharge the battery fully.

Table 7 shows some common charging rates for various styles of recharging.

Trickle chargers (charge rates lower than 0.05 C) are generally insufficient to charge a battery. They are usually only applied after a battery is fully charged (using a greater charge rate) to help offset the self-discharge rate of the battery. Batteries on a trickle charger will maintain their full charge for months at a time.

It is usually recommended that batteries on a trickle charger be fully discharged and recharged once every 6 to 12 months.

Quick and fast charging rates (over 0.2 C) can be used to charge many kinds of secondary batteries. In such cases, however, damage or 6.3 CHARGING TECHNIQUES deterioration can occur in the battery if these high charge rates are applied after the battery In general, lower charge rates will extend the has approximately 85% of its charge restored. overall life of the battery. A battery can be Many quick and damaged or defast chargers will graded if too much have currentcurrent is applied The key issue in charging a battery limiters built into during the charging them that will process. Also, is knowing when to stop charging. slowly reduce the when a battery is in current as the the final stages of battery is charged, thereby preventing most of charging, the current must be reduced to this deterioration. prevent damage to the battery. Many chargers offer current-limiting devices that will shut off The recharge times shown in Table 7 may be or reduce the applied current when the battery somewhat lower than the actual times required reaches a certain percent of its charged to recharge batteries at the associated charge potential. rates. Various elements, such as temperature, humidity, initial charge state, and the recharge Slow charge rates (between 0.05 C and 0.1 C) are the most-often recommended charge rate, history of the cell, will each act to extend the time needed to charge the cell fully. since a battery can be recharged in less than a day, without significant probability of damaging or degrading the battery. Slow 6.4 CHARGING LEAD-ACID BATTERIES charge rates can be applied to a battery for an Constant potential charging, with current indefinite period of time, meaning that the limiting, is usually recommended for sealed battery can be connected to the charger for lead-acid cells. Due to the sloping voltage days or weeks with no need for special shutprofile of a lead-acid battery, the voltage of off or current-limiting equipment on the the battery is a reliable indicator of its state of charger.

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New Technology Batteries Guide

charge. Current limiting may be accomplished through the use of a current-limiting resistor.

One manufacturer uses a miniature light bulb as a current-limiting resistor. The brightness of the bulb will provide a visual indication of the state of charge of the battery. In modern practice, however, current limiting is accomplished with integrated circuits.

6.5 CHARGING NI-CD BATTERIES During their recharge cycle, nickel-cadmium batteries react in a manner different from other batteries. Nickel-cadmium batteries will actually absorb heat during the first 25% of the charge cycle (as opposed to most secondary batteries, which generate heat all through their recharge cycle). Beyond that first quarter of the charge cycle, a Ni-Cd battery will generate heat. If constant current is applied past the point when the battery reaches approximately 85% of its fully charged state, the excess heat will cause “thermal runaway” to occur. Under thermal runaway conditions, the excess heat in the battery will cause its voltage to drop. The drop in voltage will cause the charge rate to increase (according to Ohm’s Law), generating more heat and accelerating the cycle. The temperature and internal pressure of the battery will continue to rise until permanent damage results.

When using trickle or slow chargers to charge Ni-Cd batteries, the heat build-up is minimal and is normally dissipated by atmospheric convection before thermal runaway can occur.

Most chargers supplied with, or as a part of, rechargeable devices (sealed flashlights, minivacuums, etc.) are slow chargers.

Quick or fast battery chargers, designed especially for Ni-Cd batteries, will usually

have a temperature sensor or a voltage sensor that can detect when the battery is nearing thermal-runaway conditions. When nearrunaway conditions are indicated, the charger will reduce or shut off the current entering the battery.

6.6 TIMED-CHARGE CHARGING Most charging methods, described so far in this guide, allow the user to begin charging a cell regardless of its current state of charge.

One additional method can be used to charge Ni-Cd cells, but only if the cell is completely discharged. It is called the timed-charged method.

One characteristic of Ni-Cd cells is that they can accept very large charge rates (as high as 20 C), provided that the cell is not forced into an overcharge condition.

The timed-charge charger will provide highrate current to the cell for a very specific period. A timer will then cut off the charging current at the end of that period. Some cells can be charged completely in as little as 10 minutes (as opposed to 8 hours on a slow charger).

Great care should be exercised when using a timed-charge charger, because there is no room for error. If the cell has any charge in it at all at the beginning of the charge cycle, or if the cell’s capacity is less than anticipated, the cell can quickly reach the fully charged state, proceed into thermal-runaway conditions, and cause the explosion or destruction of the cell.

Some timed-charge chargers have a special circuit designed to discharge the cell completely before charging it. These are 37

New Technology Batteries Guide

called dumped timed-charge chargers, since they dump any remaining charge before applying the timed charge.

6.7 PULSED CHARGE-DISCHARGE CHARGERS This method of charging Ni-Cd cells applies a relatively high charge rate (approximately 5 C) until the cell reaches a voltage of 1.5 V. The charging current is then removed and the cell is rapidly discharged for a brief period of time (usually a few seconds). This action depolarizes the cell components and dissipates any gaseous buildup within the cell. The cell is then rapidly charged back to 1.5 V. The process is repeated several more times until the cell’s maximum charge state is reached.

Unfortunately, this method has some difficulties. The greatest difficulty is that the maximum voltage of a Ni-Cd cell will vary with several outside factors such as the cell’s recharge history and the ambient temperature at the charger’s location. Since the cell’s maximum potential voltage is variable, the level to which it must be charged is also variable. Integrated circuits are being designed, however, that may compensate for such variations.

6.8 CHARGING BUTTON BATTERIES Secondary cylindrical (household) cells will usually have a safety seal or vent built into them to allow excess gases, created during the charging process, to escape. Secondary, button-type batteries do not have such seals and are often hermetically sealed.

When cylindrical cells are overcharged, excess gases are vented. If a button battery is inadvertently overcharged, the excess gases 38

cannot escape. The pressure will build up and will damage the battery or cause an explosion.

Care should be taken not to overcharge a secondary button battery.

6.9 INTERNAL CHARGERS For some applications, the charger may be provided, by the battery manufacturer, as an integral part of the battery itself. This design has the obvious advantage of ensuring that the correct charger is used to charge the battery, but this battery-charger combination may result in size, weight and cost penalties for the battery.

6.10 BATTERY TESTERS A battery tester is a device that contains a small load and attaches across the terminals of a battery to allow the user to see if the battery is sufficiently charged. A simple battery tester can be made from a flashlight bulb and two pieces of wire. Flashlight bulbs are ideal for testing household batteries, since the voltage and current required to light the bulb is the same as that of the battery. This kind of flashlight-bulb tester can also be used to drain a secondary battery safely before fully charging it.

Some off-the-shelf household batteries are sold with their own testers. These testers are attached to the packaging material or to the battery itself. The active conductor in the tester is covered by a layer of heat-sensitive ink. As the ends of the tester are pressed against the battery terminals, a small amount of current will flow through the material under the ink, heating it. The heating will cause the ink to change color, indicating that the battery still has energy.

New Technology Batteries Guide

Using a simple battery tester to test a Ni-Cd battery can be somewhat misleading, since a Ni-Cd battery has a flat voltage profile. The tester will indicate near-maximum voltage whether the battery is 100% charged or 85% discharged.

6.11 “SMART” BATTERIES Many battery-powered devices require the use of multi-cell battery packs (i.e., several ordinary battery cells strapped together to be used as a single unit). The individual cells cannot be charged or measured separately, without destroying the battery pack.

A new development in rechargeable battery technology is the use of microelectronics in battery-pack cases to create “intelligent” battery packs. These “smart” battery packs contain a microprocessor, memory, and sensors that monitor the battery’s temperature, voltage, and current. This information can be relayed to the device (if the device is designed to accept the information) and used to calculate the battery’s state of charge at any time or to predict how much longer the device can operate. The microprocessor on a battery pack may also record the history of the battery and display the dates and number of times that it has been charged.

To get the maximum potential from a secondary battery, the user must adopt a strict regimen of noting certain information about the battery and acting upon that information.

For example, if a battery is already partially discharged, using it in a device will obviously not allow the device to be used for its entire duty cycle. Attempting to charge a battery when the ambient temperature is too high is another example of suboptimal battery usage,

since the battery will not hold as much charge as it would have had it been charged at the recommended temperature.

Most battery users are not sufficiently diligent in matters of battery maintenance. “Smart” batteries allow the battery itself to record all pertinent information and make it available to the user at a glance.

6.12 END OF LIFE All secondary batteries will eventually fail due to age, expended components, or physical damage. A battery, when properly maintained, will fail through gradual loss of capacity. To the user, this gradual failure will appear as a frequent need to change and charge the batteries. Sudden failure, usually due to physical abuse, will prevent the battery from holding any charge at all.

The physical manifestations of a gradual failure of the battery can be seen as a degradation of the separator material, dendritic growth or other misshapening of the electrodes, and permanent material loss of the active components.

The physical manifestations of a sudden failure, can be seen as the destruction of the battery components. Open-circuit failure can be induced by an applied shock to or excess vibration of the battery. As a result, the internal components of the battery may become loose or detached, causing a gap in the electrical circuit.

Short-circuit failure can be caused by an applied shock. It can also be caused by overheating or overcharging the battery. In a short-circuit failure, some part of one of the 39

New Technology Batteries Guide

electrodes pierces (caused by shock) or grows through (caused by overcharging) the separator material in the electrolyte. This piercing effect will cause the electrical path to be shorted.

If a battery and its replacements seem to be suffering repeated premature failures, in reoccurring and similar circumstances, the failed batteries should be sent to a laboratory for dissection and analysis. The problem may lie in faulty equipment, inappropriate battery usage, or in physical abuse to the device and its batteries. Resolution of the problem will save time and money in future battery designs and applications.

6.13 BATTERY ADAPTERS A battery adapter is a device that can be used instead of a battery to provide current to a battery-powered device.

Most battery adapters will convert 60 Hz, 110 V, alternating current (i.e., typical house current) into direct current (dc) for use by battery-powered devices. Other adapters are designed to be powered by 12 V automobile batteries, usually by insertion of a plug into the automobileâ&#x20AC;&#x2122;s cigarette lighter.

40

An adapter will usually have a dc-output plug that is inserted into the battery-powered device to provide dc current to the device.

Usually, manufacturers of the more expensive battery-powered devices (e.g., cellular phones, laptop computers) will provide the customer with a battery adapter designed especially for that device. The adapter will plug into a special connector in the device to provide it power. If designed to do so, the battery adapter will charge the deviceâ&#x20AC;&#x2122;s batteries as well.

Other manufacturers make generic battery adapters. These adapters will have a batteryshaped appendage that plugs into a batterypowered device in place of a real battery and will provide energy equivalent to a real battery. While this kind of adapter has some advantages (it can be used for any battery powered device, it can be used when no charged batteries are available, etc.), those advantages are usually outweighed by the disadvantages (the power cord is inconvenient and negates the portability of the device, the battery cover cannot be replaced while the cord is attached, a multiple-battery device would require multiple adapters, etc.).

7. Products and Suppliers Table 8. Some On-Line Information Available via the World Wide Web Batteries and Battery Manufacturers Web Address battery manufacturers and Battery Engineering http://www.batteryeng.com/ suppliers listed or Duracell Batteries http://www.duracell.com/ mentioned in this section, and Eveready Batteries http://www.eveready.com/ elsewhere in this Kodak Corporation http://www.kodak.com/ guideline, are listed for the convenience NEXcell http://www.battery.com.tw/ of the reader. The Panasonic Batteries http://www.panasonic-batteries.be/home.html name of a specific product or PolyStor Corporation http://www.polystor.com/ company does not Radio Shack http://www.radioshack.com/ imply that the product or Rayovac Batteries http://www.rayovac.com/ company is, Sony Corporation http://www.sel.sony.com/SEL/rmeg/batteries/ necessarily, the best for any particular Battery Distributors Web Address application or Battery-Biz, Inc. http://www.battery-biz.com/battery-biz/ device. The lists Battery Depot http://www.battery-depot.com/ are, necessarily, not all-inclusive. The Battery Network http://batnetwest.com/ list of Web pages Batteries Plus http://www.spromo.com/battplus/ was compiled following a Web E-Battery http://e-battery.com/ search performed in Powerline http://www.powerline-battery.com/ August, 1997. New All Web information was verified in August, 1997.

Web pages may have appeared since then and some which appear in this list may no longer 7.1 BATTERY MANUFACTURERS be available. Other Web pages, that were not The battery manufacturers listed below are listed in the Web-search database at that time, some of the manufacturers of household will also not appear in this list. batteries. They are presented in alphabetical

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New Technology Batteries Guide

order. All information was verified in August, 1997.

Email Address: bunny@chas.ts.maritz.com

7.1.1 Battery Engineering Postal Address: Battery Engineering, Inc. 100 Energy Drive Canton, MA 02001 Phone Number: (617) 575-0800 Web Page: http://www.batteryeng.com Email Address: info@batteryeng.com

7.1.4 Rayovac Postal Address: Rayovac Corporation P.O. Box 44960 Madison, WI 53744-4960 Phone Number: 1 (800) 237-7000 Web Page: http://www.rayovac.com/ Email Address: customers@rayovac.com

7.1.2 Duracell Postal Address: Duracell, Inc. Berkshire Corp Park Bethel, CT 06801 Phone Number: 1 (800) 551-2355 Web Page: http://www.duracell.com/ 7.1.3 Eveready Postal Address: Eveready Battery Company, Inc. Checkerboard Square St. Louis, MO 63164-0001 Phone Number: 1 (800) 383-7323 Web Page: http://www.eveready.com/

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8. A Glossary of Battery Terms 2 Ampere-Hour -- One ampere-hour is equal to a current of one ampere flowing for one hour. A unit-quantity of electricity used as a measure of the amount of electrical charge that may be obtained from a storage battery before it requires recharging.

2 Ampere-Hour Capacity -- The number of ampere-hours which can be delivered by a storage battery on a single discharge. The ampere-hour capacity of a battery on discharge is determined by a number of factors, of which the following are the most important: final limiting voltage; quantity of electrolyte; discharge rate; density of electrolyte; design of separators; temperature, age, and life history of the battery; and number, design, and dimensions of electrodes.

2 Anode -- In a primary or secondary cell, the metal electrode that gives up electrons to the load circuit and dissolves into the electrolyte.

2 Aqueous Batteries -- Batteries with waterbased electrolytes.

2 Available Capacity -- The total battery capacity, usually expressed in amperehours or milliampere-hours, available to perform work. This depends on factors such as the endpoint voltage, quantity and density of electrolyte,

temperature, discharge rate, age, and the life history of the battery.

2 Battery -- A device that transforms chemical energy into electric energy.

The term is usually applied to a group of two or more electric cells connected together electrically. In common usage, the term â&#x20AC;&#x153;batteryâ&#x20AC;? is also applied to a single cell, such as a household battery.

2 Battery Types -- There are, in general, two type of batteries: primary batteries, and secondary storage or accumulator batteries. Primary types, although sometimes consisting of the same active materials as secondary types, are constructed so that only one continuous or intermittent discharge can be obtained. Secondary types are constructed so that they may be recharged, following a partial or complete discharge, by the flow of direct current through them in a direction opposite to the current flow on discharge. By recharging after discharge, a higher state of oxidation is created at the positive plate or electrode and a lower state at the negative plate, returning the plates to approximately their original charged condition.

2 Battery Capacity -- The electric output of a cell or battery on a service test 43

New Technology Batteries Guide

delivered before the cell reaches a specified final electrical condition and may be expressed in ampere-hours, watt-hours, or similar units. The capacity in watt-hours is equal to the capacity in ampere-hours multiplied by the battery voltage.

2 Battery Charger -- A device capable of supplying electrical energy to a battery.

2 Battery-Charging Rate -- The current expressed in amperes at which a storage battery is charged.

2 Battery Voltage, final -- The prescribed lower-limit voltage at which battery discharge is considered complete. The cutoff or final voltage is usually chosen so that the useful capacity of the battery is realized. The cutoff voltage varies with the type of battery, the rate of discharge, the temperature, and the kind of service in which the battery is used. The term “cutoff voltage” is applied more particularly to primary batteries, and “final voltage” to storage batteries. Synonym: Voltage, cutoff.

2 Ci -- The rated capacity, in ampere-hours, for a specific, constant discharge current (where i is the number of hours the cell can deliver this current). For example, the C5 capacity is the ampere-hours that can be delivered by a cell at constant current in 5 hours. As a cell’s capacity is not the same at all rates, C5 is usually less than C20 for the same cell.

44

2 Capacity -- The quantity of electricity delivered by a battery under specified conditions, usually expressed in ampere-hours.

2 Cathode -- In a primary or secondary cell, the electrode that, in effect, oxidizes the anode or absorbs the electrons.

2 Cell -- An electrochemical device, composed of positive and negative plates, separator, and electrolyte, which is capable of storing electrical energy. When encased in a container and fitted with terminals, it is the basic “building block” of a battery.

2 Charge -- Applied to a storage battery, the conversion of electric energy into chemical energy within the cell or battery. This restoration of the active materials is accomplished by maintaining a unidirectional current in the cell or battery in the opposite direction to that during discharge; a cell or battery which is said to be charged is understood to be fully charged.

2 Charge Rate -- The current applied to a secondary cell to restore its capacity.

This rate is commonly expressed as a multiple of the rated capacity of the cell. For example, the C/10 charge rate of a 500 Ah cell is expressed as, C/10 rate = 500 Ah / 10 h = 50 A. 2 Charge, state of -- Condition of a cell in terms of the capacity remaining in the cell.

New Technology Batteries Guide

2 Charging -- The process of supplying electrical energy for conversion to stored chemical energy.

2 Discharge -- The conversion of the chemical energy of the battery into electric energy.

2 Constant-Current Charge -- A charging process in which the current of a storage battery is maintained at a constant value. For some types of leadacid batteries this may involve two rates called the starting and finishing rates.

2 Discharge, deep -- Withdrawal of all electrical energy to the end-point voltage before the cell or battery is recharged.

2 Constant-Voltage Charge -- A charging process in which the voltage of a storage battery at the terminals of the battery is held at a constant value.

2 Cycle -- One sequence of charge and discharge. Deep cycling requires that all the energy to an end voltage established for each system be drained from the cell or battery on each discharge. In shallow cycling, the energy is partially drained on each discharge; i.e., the energy may be any value up to 50%.

2 Cycle Life -- For secondary rechargeable cells or batteries, the total number of charge/discharge cycles the cell can sustain before it becomes inoperative.

In practice, end of life is usually considered to be reached when the cell or battery delivers approximately 80% of rated ampere-hour capacity.

2 Depth of Discharge -- The relative amount of energy withdrawn from a battery relative to how much could be withdrawn if the battery were discharged until exhausted.

2 Discharge, high-rate -- Withdrawal of large currents for short intervals of time, usually at a rate that would completely discharge a cell or battery in less than one hour.

2 Discharge, low-rate -- Withdrawal of small currents for long periods of time, usually longer than one hour.

2 Drain -- Withdrawal of current from a cell.

2 Dry Cell -- A primary cell in which the electrolyte is absorbed in a porous medium, or is otherwise restrained from flowing. Common practice limits the term â&#x20AC;&#x153;dry cellâ&#x20AC;? to the LeclanchĂŠ cell, which is the common commercial type.

2 Electrochemical Couple -- The system of active materials within a cell that provides electrical energy storage through an electrochemical reaction.

2 Electrode -- An electrical conductor through which an electric current enters or leaves a conducting medium, whether it be an electrolytic solution, solid, molten mass, gas, or vacuum.

For electrolytic solutions, many solids, and molten masses, an electrode is an 45

New Technology Batteries Guide

electrical conductor at the surface of which a change occurs from conduction by electrons to conduction by ions. For gases and vacuum, the electrodes merely serve to conduct electricity to and from the medium.

2 Electrolyte -- A chemical compound which, when fused or dissolved in certain solvents, usually water, will conduct an electric current. All electrolytes in the fused state or in solution give rise to ions which conduct the electric current.

2 Electropositivity -- The degree to which an element in a galvanic cell will function as the positive element of the cell. An element with a large electropositivity will oxidize faster than an element with a smaller electropositivity.

2 End-of-Discharge Voltage -- The voltage of the battery at termination of a discharge.

2 Energy -- Output capability; expressed as capacity times voltage, or watt-hours.

2 Energy Density -- Ratio of cell energy to weight or volume (watt-hours per pound, or watt-hours per cubic inch).

2 Float Charging -- Method of recharging in which a secondary cell is continuously connected to a constantvoltage supply that maintains the cell in fully charged condition.

2 Galvanic Cell -- A combination of electrodes, separated by electrolyte, 46

that is capable of producing electrical energy by electrochemical action.

2 Gassing -- The evolution of gas from one or both of the electrodes in a cell.

Gassing commonly results from selfdischarge or from the electrolysis of water in the electrolyte during charging.

2 Internal Resistance -- The resistance to the flow of an electric current within the cell or battery.

2 Memory Effect -- A phenomenon in which a cell, operated in successive cycles to the same, but less than full, depth of discharge, temporarily loses the remainder of its capacity at normal voltage levels (usually applies only to Ni-Cd cells).

2 Negative Terminal -- The terminal of a battery from which electrons flow in the external circuit when the cell discharges. See Positive Terminal.

2 Nonaqueous Batteries -- Cells that do not contain water, such as those with molten salts or organic electrolytes.

2 Ohmâ&#x20AC;&#x2122;s Law -- The formula that describes the amount of current flowing through a circuit.

Voltage = Current Ă&#x2014; Resistance.

2 Open Circuit -- Condition of a battery which is neither on charge nor on discharge (i.e., disconnected from a circuit).

New Technology Batteries Guide

2 Open-Circuit Voltage -- The difference in potential between the terminals of a cell when the circuit is open (i.e., a noload condition).

2 Oxidation -- A chemical reaction that results in the release of electrons by an electrodeâ&#x20AC;&#x2122;s active material.

2 Parallel Connection -- The arrangement of cells in a battery made by connecting all positive terminals together and all negative terminals together, the voltage of the group being only that of one cell and the current drain through the battery being divided among the several cells. See Series Connection.

2 Polarity -- Refers to the charges residing at the terminals of a battery.

2 Positive Terminal -- The terminal of a battery toward which electrons flow through the external circuit when the cell discharges. See Negative Terminal.

2 Primary Battery -- A battery made up of primary cells. See Primary Cell.

2 Primary Cell -- A cell designed to produce electric current through an electrochemical reaction that is not efficiently reversible. Hence the cell, when discharged, cannot be efficiently recharged by an electric current.

Note: When the available energy drops to zero, the cell is usually discarded.

Primary cells may be further classified by the types of electrolyte used.

2 Rated Capacity -- The number of amperehours a cell can deliver under specific conditions (rate of discharge, end voltage, temperature); usually the manufacturerâ&#x20AC;&#x2122;s rating.

2 Rechargeable -- Capable of being recharged; refers to secondary cells or batteries.

2 Recombination -- State in which the gases normally formed within the battery cell during its operation, are recombined to form water.

2 Reduction -- A chemical process that results in the acceptance of electrons by an electrodeâ&#x20AC;&#x2122;s active material.

2 Seal -- The structural part of a galvanic cell that restricts the escape of solvent or electrolyte from the cell and limits the ingress of air into the cell (the air may dry out the electrolyte or interfere with the chemical reactions).

2 Secondary Battery -- A battery made up of secondary cells. See Storage Battery; Storage Cell.

2 Self Discharge -- Discharge that takes place while the battery is in an opencircuit condition.

2 Separator -- The permeable membrane that allows the passage of ions, but prevents electrical contact between the anode and the cathode.

2 Series Connection -- The arrangement of cells in a battery configured by connecting the positive terminal of 47

New Technology Batteries Guide

each successive cell to the negative terminal of the next adjacent cell so that their voltages are cumulative. See Parallel Connection.

2 Shelf Life -- For a dry cell, the period of time (measured from date of manufacture), at a storage temperature of 21(C (69(F), after which the cell retains a specified percentage (usually 90%) of its original energy content.

2 Short-Circuit Current -- That current delivered when a cell is short-circuited (i.e., the positive and negative terminals are directly connected with a low-resistance conductor).

2 Starting-Lighting-Ignition (SLI) Battery -- A battery designed to start internal combustion engines and to power the electrical systems in automobiles when the engine is not running. SLI batteries can be used in emergency lighting situations.

2 Stationary Battery -- A secondary battery designed for use in a fixed location.

2 Storage Battery -- An assembly of identical cells in which the electrochemical action is reversible so that the battery may be recharged by passing a current through the cells in the opposite direction to that of discharge. While many non-storage batteries have a reversible process, only those that are economically rechargeable are classified as storage batteries. Synonym: Accumulator; Secondary Battery. See Secondary Cell.

48

2 Storage Cell -- An electrolytic cell for the generation of electric energy in which the cell after being discharged may be restored to a charged condition by an electric current flowing in a direction opposite the flow of current when the cell discharges. Synonym: Secondary Cell. See Storage Battery.

2 Taper Charge -- A charge regime delivering moderately high-rate charging current when the battery is at a low state of charge and tapering the current to lower rates as the battery becomes more fully charged.

2 Terminals -- The parts of a battery to which the external electric circuit is connected.

2 Thermal Runaway -- A condition whereby a cell on charge or discharge will destroy itself through internal heat generation caused by high overcharge or high rate of discharge or other abusive conditions.

2 Trickle Charging -- A method of recharging in which a secondary cell is either continuously or intermittently connected to a constant-current supply that maintains the cell in fully charged condition.

2 Vent -- A normally sealed mechanism that allows for the controlled escape of gases from within a cell.

2 Voltage, cutoff -- Voltage at the end of useful discharge. (See Voltage, endpoint.)

New Technology Batteries Guide

2 Voltage, end-point -- Cell voltage below which the connected equipment will not operate or below which operation is not recommended.

2 Voltage, nominal -- Voltage of a fully charged cell when delivering rated current.

2 Wet Cell -- A cell, the electrolyte of which is in liquid form and free to flow and move.

49

New Technology Batteries Guide

50

9. Bibliography American National Standard Specification for Dry Cells and Batteries, American National Standards Institutes, Inc. ANSI C18.1M-1992.

Application Notes & Product Data Sheet: Primary Batteriesâ&#x20AC;&#x201D;Alkaline, Heavy Duty & General Purpose, Rayovac Corporation, January 1996.

Batteries Used with Law Enforcement Communications Equipment: Chargers and Charging Techniques, W.W. Scott, Jr., U.S. Department of Justice, LESP-RPT-0202.00, June 1973.

Batteries Used with Law Enforcement Communications Equipment: Comparison and Performance Characteristics, R.L. Jesch and I.S. Berry, U.S. Department of Justice, LESP-RPT-0201.00, May 1972.

Battery Engineering Web Site, http://www.batteryeng.com, August 1997.

Battery Selection & Care, Eveready Battery Corporation, 1995.

Camcorder Battery Pocket Guide, Eveready Battery Corporation, Inc., 1996.

Design Note: Renewal Reusable Alkaline Batteries Applications and System Design Issues For Portable Electronic Equipment, Rayovac Corporation, presented at: Portable by Design Conference, 1995.

Duracell Batteries Web Site, http://www.duracell.com, August 1997.

Easy to Choose, Easy to Use, Eveready Battery Corporation, 1997.

Encyclopedia of Physical Science and Technology, Brooke Schumm, Jr., 1992.

Eveready and the Environment, Eveready Battery Company, Inc., 1995.

Eveready Batteries Web Site, http://www.eveready.com, August 1997.

Household Batteries and the Environment, Rayovac Corporation, 1995.

How to Choose, Use, Care For, and Dispose of Batteries, Electronics Industries Association Consumer Electronics Group, 1992.

Cellular Duracell Rechargeable Batteries, Duracell, 1996.

51

New Technology Batteries Guide

Land Mobile FM or PM Communications Equipment, Measurement and Performance Standard, Electronics Industry Association/ Telecommunications Industry Association, Publication EIA/TIA 603, 1993.

Minimum Standards for Portable/Personal Land Mobile Communications FM or PM Equipment 25-470 MC, Electronics Industries Association, EIA/TIA-316-C-1989.

Navy Primary and Secondary Batteries.

Design and Manufacturing Guidelines, NAVSO P-3676, September 1991.

Panasonic Batteries Web Site, http://www.panasonic-batteries.be/ho me.html, August 1997.

PolyStor Web Page, http://www.polystor.com, August, 1997.

Rayovac Batteries Web Site, http://www.rayovac.com, August 1997.

Rechargeable Batteries for Personal/Portable Transceivers, National Institute of Justice, NIJ Standard-0211.01, September, 1995.

Return of the Straight Dope, Cecil Adams, Chicago Reader, 11 East Illinois Street, Chicago, IL 60611, 1994.

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Supervisory ICs Empower Batteries to Take Charge, Bill Schweber, EDN, Cahners Publishing Company, 8773 South Ridgeline Blvd., Highlands Ranch, CO 80126-2329, September 1, 1997.

Telephonyâ&#x20AC;&#x2122;s Dictionary, second edition, April 1986. Graham Langley, Telephony Publishing Corp.

The Eveready Battery Story, Eveready Battery Company, Inc., 1995.

The Story of Packaged Power, Duracell International, Inc., July, 1995.

Van Nostrandâ&#x20AC;&#x2122;s Scientific Encyclopedia, Sixth Edition, Douglas M Considine, Editor, 1983.

What is a Battery?, Rayovac Corporation, 1995.

Why Use Energizer AA Lithium Batteries?, Eveready Battery Company, Inc., 1993.