LAUSR

LiCoO2/graphite full-cells with a carbonate-free electrolyte based on lithium bis(fluorosulfonyl)imide and sulfolane (LiFSI/SL) show excellent cycle stability at high temperatures. In this study, we used X-ray photoelectron spectroscopy to investigate the composition of the solid electrolyte interface (SEI) layer on the surface of the positive and negative electrodes of a cell containing LiFSI/SL cycled at high temperature. Inorganic species, such as LiF and sulfonyl compounds, were observed in the SEI on the surface of both the positive and negative electrodes of cells with LiFSI/SL. The SEI derived from LiFSI on the positive electrode suppressed not only oxidative electrolyte decomposition but also crystal structure change of LiCoO2. Moreover, the SEI on the negative electrode controlled severe reductive decomposition of the electrolytes.