Cycling performance and surface analysis of Lithium bis(trifluoromethanesulfonyl)imide in propylene carbonate with graphite

The performance of different concentrations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in propylene carbonate (PC) on a binder free (BF) graphite electrode has been investigated. Variation in the salt concentration results in a change in the reduction reactions at the electrode interface and the reversible cycling of the cell. Continuous electrolyte reduction is observed at low salt concentrations while reversible lithiation/delithiation is observed at high salt concentrations. Ex-situ surface analysis of the cycled electrodes has been conducted via infrared spectroscopy with attenuated total reflectance (IR-ATR) and X-ray photoelectron spectroscopy (XPS). The ex-situ surface analysis suggests that changes in the cycling performance correlate with changes in the composition of the solid electrolyte interface (SEI) on the surface of binder free (BF) graphite electrode. The improved cycling performance correlates with an increase in the LiF content of the SEI.