New Insight into Vinylethylene Carbonate as a Film Forming Additive to Ethylene Carbonate-Based Electrolytes for Lithium-Ion Batteries

The effects of vinylethylene carbonate (VEC) as electrolyte additive and the content of VEC in ethylene carbonate (EC)-based electrolyte on the formation mechanisms of solid electrolyte interphase (SEI) film and the electrochemical properties of the graphite electrodes in lithium-ion batteries are investigated by cyclic voltammetry (CV) measurement and charge-discharge test. Enhanced electrochemical performance is observed for graphite electrodes in VEC-containing electrolytes with low content. Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy are used to investigate the morphology and the surface chemistry of graphite electrodes cycled in VEC-free and VEC-containing electrolytes. Finally, electrochemical impedance spectroscopy (EIS) is used in order to better understand the formation mechanisms of SEI film in VEC-containing electrolyte. The results reveal that the main reduction products of the SEI film formed in VEC-containing electrolyte are VEC polymerizes, Li2CO3 and ROCO2Li. The SEI film covering graphite electrodes in VEC-containing electrolyte can be more stable during lithium ions insertion, and be flexible to accommodate the volume changes of graphite material, resulting in a better reversibility of lithium ions insertion and extraction.