Film formation and cycleability of LiBOB-based electrolyte

The formation of solid electrolyte interphase (SEI) film on graphite in a lithium bis(oxalato)borate (LiBOB)- based electrolyte was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The effects of SEI film on the cycleabilities of graphite were examined at room temperature (25 °C) and at high temperature (70 °C). Results showed that the SEI film was formed at around 1.7 V and BOB^- ions were reduced to oxalate, which was one of the components of the SEI film. EIS showed that the impedance of the SEI film decreased during the charge/discharge cycle and this was favorable for cycle stability. Whether it was at room temperature or at high temperature, the graphite had better cycleability in the LiBOB-based electrolyte than in the LiPF₆-based electrolyte.