Carbonate Free Electrolyte for Lithium Ion Batteries Containing γ-Butyrolactone and Methyl Butyrate

A novel carbonate free electrolyte, 1 M lithium difluoro(oxalato) borate (LiDFOB) in 1:1 gamma -butyrolactone (GBL)/methyl butyrate (MB), has been compared to a standard electrolyte, 1 M LiPF 6 in 1:1:1 EC/DMC/DEC, and a 1 M LiDFOB in 1:1:1 EC/DMC/DEC electrolyte. The conductivity of 1 M LiDFOB in GBL/MB is higher at low temperature, but slightly lower at higher temperature compared to the standard electrolyte. The 1 M LiDFOB in GBL/MB electrolyte has comparable cycling performance to the standard electrolyte, and better cycling performance than the 1 M LiDFOB in EC/DMC/DEC electrolyte. The reversible cycling performance suggests that the LiDFOB in GBL/MB electrolyte forms a stable anode solid electrolyte interface (SEI) in the presence of GBL. Ex-situ surface analysis of the extracted electrodes has been conducted via a combination of XPS, FTIR-ATR and SEM which suggests that the stable anode SEI results is primarily composed of reduction products of LiDFOB.