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ENERGY STORAGE
Li-ion battery concerns for safe usage The high energy and power density provided by Li-ion battery chemistry also carries with it the propensity to turn catastrophic if not designed, charged or used in an appropriate manner. Dr Judy Jeevarajan, Research Director, Electrochemical Safety - Underwriters Laboratories Inc., talks about various risk factors and challenges regarding battery safety that need to be addressed for safe usage.
E
nergy storage in the form of batteries have become an essential part of our everyday life. With their use in consumer devices such as mobile phones, cameras, camcorders, and laptops, to their use in larger applications as in the areas of space, marine, EVs and grid energy storage, the battery energy storage systems have greatly enriched our lives. Of the many battery chemistries that have been in existence, the lithium-based systems have held the market the longest and continue to do so today. Of the lithium-based systems, the rechargeable Li-ion batteries are more commonly used in the applications stated above. Li-ion batteries provide high power and energy and have a long cycle life and calendar life. Due to the proliferation of cell and
battery manufacturing companies and due to myriad cell and battery models manufactured today, the risks associated with this battery chemistry has increased. The high energy and power density provided by this battery chemistry also carries with it the propensity to turn catastrophic if not designed, charged or used in an appropriate manner. Li-ion batteries were first commercialized by Sony in the early 1990s, used in small consumer portable electronic devices. These applications required the use of two to a maximum of eight cells in the battery pack. Today, the batteries that are manufactured for several applications are configured with hundreds to thousands of cells. The cells that constitute the battery packs also come in different sizes and are available in at least three different form factors, namely, the cylindrical, prismatic metal can and prismatic pouch formats. The batteries also come in numerous sizes to meet the energy, power, volume and weight demands of the various applications. In addition to this, several cathode, anode, electrolyte and separator combinations can be used to construct a single-cell model, which makes an understanding of the safety characteristics more challenging.
Low quality factor
Dr Judy Jeevarajan
With the high demand for batteries of this chemistry, the cell and battery manufacturing industry has been made into a lucrative business wherein low quality cells and batteries exist in abundance. Some of these low quality cells can | September-October 2020
be purchased online at an inexpensive price and quick turnaround time. The low quality cells often times do not provide the required performance but the bigger concern is that they do not have the required safety features that are traditionally used internally in cells manufactured by the OEMs. The same is true for batteries that may be designed with less than required safety controls. This factor not only increases the risk to the user but also increases the risk to the transportation industry that provides the shipment of the cells and batteries. The hazard causes for Li-ion batteries can be categorized broadly into thermal, mechanical and electrical types (Figure 1). Given the wide expanse of the usage of these cells and batteries, makes the installation and use of this chemistry in large megawatthour (MWh) to gigawatt-hour (GWh) size grid energy storage systems more challenging, especially when used in extreme climatic environments.
Large-scale battery testing
The size of these large installations poses a bigger challenge when it comes to testing, wherein the entire system cannot be tested beyond its limits to characterize safety due to the time and cost factors involved in such large scale offnominal tests. Consequently, the grid energy storage industry has witnessed several large-scale battery fires. Safety characteristics of a single Li-ion cell does not translate directly to the safety of a larger battery configuration using the same cells.
