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, HCO 2 Li, Li x SO y and Li 2 S (or Li 2 S 2 ) 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 HCO 2 Li are solvent degradation products existed in electrolyte. The reversibility of Li 2 S and Li 2 S 2 are not serious as in previous reports. ROLi, HCO 2 Li and Li x SO y co-deposited with Li 2 S or Li 2 S 2 in discharge process lead to the cathodes performance deterioration. Lithium salts such as LiNO 3 and LiTFSI can oxidize sulfur compounds to higher oxidation states, and Li x SO y species increased with cycling indicates the active mass irreversible oxidation that may be another important reason for the capacity fading of Li-S battery.