Fundamental electrolyte characterization is a vital portion of current research being conducted in the field of energy storage. This is a direct consequence of the electrolyte’s critical role in maintaining secondary batteries’ stability and performance. A widely adoptable characterization technique for electrolytes will be easy to use, involve commonly accessible instrumentation, and permit accurate identification. Our characterization process with nuclear magnetic resonance (NMR) could be more widely implemented in electrolyte degradation studies. This research utilizes NMR spectroscopy to study how the electrolyte decays with time and with small additions of water. This experimental method allows for evaluation of electrolytes without risk of contamination from deuterated reference solvents. Degradation of carbonates and salts with a varying amounts of water or HF have been studied for sodium electrolyte systems. As anticipated the sodium system shows a much lower rate of decomposition compared to lithium systems, and so degradation was accelerated with the addition of heat. In addition to pure electrolytes, additives were also studied and proved to alter degradation rate and the byproducts formed. For example, the fluorinated phosphazene co-solvent named FM2 shows an improved thermal and safety performance in battery electrolytes. Our results indicate that the additive acts as a “HF scavenger” in wet electrolytes. Commonly used sodium electrolytes with FM2 additive didn’t show a peak from -180 to -190 ppm, which would be indicative of free fluorine ion. This characterization method provides more information than using the traditional technique of studying the cycling performance of the electrolyte, which gives us a better understanding of the quantity of decomposition observed. Included is a demonstration of the utility and benefits of the described method for real time electrolyte evaluation.

Sodium electrolyte degradation: Evaluating pure electrolyte degradation through a safe and convenient NMR technique

253rd National Meeting (2017)

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