Effect of Fluoroethylene Carbonate on Electrochemical Performances of Lithium Electrodes and Lithium-Sulfur Batteries

The positive impact of a fluoroethylene carbonate (FEC) solvent on the interfacial stability of Li metal electrodes and the electrochemical performance of lithium-sulfur (Li-S) cells is investigated. To confirm the effects of FEC on electrolyte decomposition and cell resistance, the surface chemistry and impedance of an Li electrode cycled in electrolytes with and without a FEC solvent are investigated using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectrometry (ToF-SIMS), and electrochemical impedance spectroscopy. A protective layer with a FEC solvent for the formation of robust SEI and carbonate-based solvents for the suppression of polysulfide attack against an Li anode was formed on the Li anode by UV-curing polymerization. It is found that the protective layer with FEC effectively suppresses the significant overcharge by the shuttle process of polysulfide species and improves cycling performance of Li-S cells.