Synthesis and Electrolyte Study of Lithium Bis(perfluorinated pinacolato)Borate for Lithium‐Ion Batteries

Lithium‐ion batteries are the leading rechargeable battery technology. 1 M lithium hexafluorophosphate (LiPF6) dissolved in carbonate solvents is commonly used as the electrolyte; however, LiPF6 is hygroscopic and forms toxic HF in the presence of water. This work presents the synthesis of lithium bis(perfluorinated pinacolato)borate salts Li[B(pp)2]·xDME (x = 0 or 1, pp = perfluorinated pinacolato, O2C2(CF3)4), which exhibit superior air tolerance and have higher thermal stability than LiPF6. Lithium‐ion cycling using 1 M Li[B(pp)2]·DME and 0.2 M Li[B(pp)2] electrolyte salts was performed, where 0.2 M Li[B(pp)2] cycled with higher capacity than 1 M Li[B(pp)2]·DME. X‐ray photoelectron spectroscopy on the post‐cycled NMC cathode found a thicker cathode electrolyte interphase with less LiF when using Li[B(pp)2]·DME than for LiPF6 based electrolyte.