Insights into Li-S Battery Cathode Capacity Fading Mechanisms: Irreversible Oxidation of Active Mass during Cycling

The solid components deposited in sulfur cathode during cycling for Li-S battery is studied in this work. ROLi, HCO2Li, LixSOy and Li2S (or Li2S2) are proved to be the main components by the methods of Fourier transform infrared (FTIR), Raman spectra and X-ray photoelectron spectroscopy (XPS). ROLi and HCO2Li are solvent degradation products existed in electrolyte. The reversibility of Li2S and Li2S2 are not serious as in previous reports. ROLi, HCO2Li and LixSOy co-deposited with Li2S or Li2S2 in discharge process lead to the cathodes performance deterioration. Lithium salts such as LiNO3 and LiTFSI can oxidize sulfur compounds to higher oxidation states, and LixSOy species increased with cycling indicates the active mass irreversible oxidation that may be another important reason for the capacity fading of Li-S battery.