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.