Effects of Fluoroethylene Carbonate (FEC) on Anode and Cathode Interfaces at Elevated Temperatures

The use of electrolyte additives is one of the most effective and economical ways to improve battery performance by stabilizing the electrode/electrolyte interface. In this work, we identified that fluoroethylene carbonate (FEC), which is one of the important electrolyte additives, had different impacts on anode and cathode, by investigating a graphite anode and a LiMn2O4 cathode through electrochemical analyses at room and elevated temperatures. In the anode side, the solid electrolyte interphase (SEI) layer derived from FEC exhibited a lower interfacial resistance and excellent thermal stability, showing excellent rate capability and improved cycle retention of cells. In contrast, poor cycling retention and a rapid increase in the interfacial resistance of the cathode were observed at elevated temperature. The poorer performance of the cathode in the FEC-containing cell at elevated temperature was attributed to the formation of a thicker surface layer and to increased Mn dissolution catalyzed by HF, which resulted from FEC dehydrofluorination initiated or accelerated by elevated temperature. Accordingly, it is suggested that the amount of FEC in a full cell must be optimized to minimize the adverse effects of FEC on cathode.