Oxidation of Dimethyl Sulfoxide Solutions by Electrochemical Reduction of Oxygen

Oxygen reduction in nonaqueous electrolyte solutions containing Li salts is a complex field of research involving solution reactions with oxygen radicals and lithium oxides. The aprotic polar solvent dimethyl sulfoxide presents itself as a most promising candidate for a durable electrolyte for use in lithium–oxygen batteries. In the present study, we detail our in-depth study on dimethyl sulfoxide (DMSO) stability in the presence of electroactive lithium oxygen species on carbon electrodes. The question of the stability of DMSO is magnified by our use of carbon-fiber electrodes, which have relatively high specific surface-area and utilize low volumes of electrolyte solutions. This configuration has enabled us to identify even minor side-products such as LiOH, dimethyl sulfone, Li2SO3 and Li2SO4. The proposed mechanism of DMSO decomposition is supported by analytical measurements. These analyses confirm that during the reduction of oxygen on carbon electrodes, the solvent undergoes oxidation by reactive oxygen species and lithium oxides.