Effect of impurities and moisture on lithium bisoxalatoborate (LiBOB) electrolyte performance in lithium-ion cells

Electrolytes containing LiB(C₂O₄)₂ (LiBOB) salts are of increasing interest for lithium-ion cells for several reasons that include their ability to form a stable solid electrolyte interphase on graphite electrodes. However, cells containing these electrolytes often show inconsistent performance because of impurities in the LiBOB salt. In this work we compare cycling and impedance data from cells containing electrolytes with LiBOB that was obtained commercially and LiBOB purified by a rigorous recrystallization procedure. We relate the difference in performance to a lithium oxalate impurity that may be a residual from the salt manufacturing process. We also examine the reaction of LiBOB with water to determine the effect of salt storage in high-humidity environments. Although LiBOB electrolytes containing trace amounts (∼100 ppm) of moisture appear relatively stable, higher moisture contents (∼1 wt%) lead to observable salt decomposition resulting in the generation of B(C₂O₄)(OH) and LiB(C₂O₄)(OH)₂ compounds that do not dissolve in typical carbonate solutions and impair lithium-ion cell performance.