Electrolyte

Designing Electrolytes For Extreme Operating Conditions

Electrolyte

Designing Electrolytes For Extreme Operating Conditions

A design principle for electrolytes paves the way for high-voltage, fast-charging, wide-temperature range batteries Lithium ion batteries used in extreme applications require novel electrolytes. Ideally these electrolytes need to be non-flammable, operate over a wide voltage and temperature range range, and enable fast charging while reducing the risk of lithium plating. Xu et al developed and validated an electrolyte design strategy for high energy batteries operating under extreme conditions (±60°C). The primary criteria for solvent selection are: a low freezing point, moderate boiling point, and wide electrochemical stability. A secondary criteria is the solvating ability; the appropriate solvent system ensures low Li-ion desolvation energy while maintaining Li salt dissociation. In order to maintain ionic conductivity, soft solvents are paired with a highly dissociating lithium salt. Researchers applied their design criteria to create NMC811||graphite full cells with 1 M LiTFSI MDFA/MDFSA–TTE electrolytes. The coin cells (areal capacity >2.5 mAh cm−2) were able to operate over a wide temperature range (−60 °C to +60 °C), and the pouch cells retained >83% room-temperature capacity over 300 cycles with an average CE of more than 99.9% at −30 °C. Academia | P. 221 Source: Xu, J., Zhang, J., Pollard, T.P. et al.

The electrolyte design principle for extreme Li-ion batteries involves identifying solvents with relatively low DN (<10) and high dielectric constant (>5) which minimizes Li+/solvent binding energy while still dissociating Li salt. Adding a component with high reduction potential enables the formation of LiF-rich interphases on both electrodes, which facilitates similar lithiation/delithiation kinetics.

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