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.