Characterising Battery Materials with Benchtop NMR

Source: Dr. Cameron Chai and Peter Airey, AXT PTY LTD

Benchtop NMR is an ideal technique for research into battery materials and quality control of battery raw materials. With the ability to quantify key material concentrations in minutes, we can rapidly gain an understanding of factors affecting performance and properties of electrolytes. This information can be highly beneficial in accelerating development programs and ensuring optimal quality of final products in manufacturing.

The X-Pulse broadband benchtop NMR is a powerful instrument with a wide range of applications pertaining to battery technology. These benchtop systems supersede the massive systems that used to require highly skilled operators and can perform the same high-field NMR experiments at a fraction of the cost. The X-Pulse can resolve complex proton spectra at 60MHz field strength thanks to its better than 0.35 Hz spectral resolution at the half-height of a peak. It is unique in that it is the only benchtop NMR instrument with built-in broadband multinuclear capability, allowing users to collect spectra from the wide range of nuclei present in electrolytes, including carbon, hydrogen, sodium, boron, phosphorus, fluorine, and lithium at temperatures from 20 to 60°C.

Using NMR for Battery Electrolyte Analysis

Batteries typically have a cathode and anode separated by an electrolyte. The electrolyte is dissolved in an organic solvent such as dimethyl carbonate and ethylene carbonate and may incorporate additives to enhance performance. NMR helps the understanding of battery performance by: > Quantifying the salt and additive concentration in electrolytes to better understand energy density and to develop higher power density formulations > Measuring the transference numbers of those electrolytes and ionic conductivity by determining the diffusion coefficients of the various species in the electrolytes > Verifying raw materials purity to benchmark electrolytes > Monitoring electrolyte breakdown reactions to better understand their processes which directly affects lifespan

NMR in Quality Control of Battery Materials

By way of example, a client was supplied with 2 solvents, apparently with the same chemistry and performance, however, testing revealed otherwise, except the reasons for this were unknown. Hydrogen NMR did not reveal any discernable differences that would affect performance. Fluorine spectra, aimed at understanding the electrolyte anion coming from hexafluorophosphate lithium salt was collected and one sample displayed a doublet on the coupled spectrum. A different doublet attributed to decomposition was also observed at a different frequency. The likely cause was breakdown of the salt by hydrolysis. With this knowledge the client was able to take remedial action.