Multifunctional Catalyst CuS for Nonaqueous Rechargeable Lithium–Oxygen Batteries

Copper sulfide with flower-like (f-CuS) and carambola-like (c-CuS) morphologies was successfully synthesized by a facile one-step solvothermal route with different surfactants. When employed as cathode catalysts for lithium-oxygen batteries (LOBs), f-CuS outperforms c-CuS in terms of oxygen electrochemistry, judging from the faster kinetics and the higher reversibility of oxygen reduction/oxidation reactions, as well as the better LOB performance. Moreover, an abnormal high-potential discharge plateau was observed in the discharge profile of the LOB. To understand the different performances of f-CuS and c-CuS and the abnormal high-potential plateau, theoretical calculations were conducted, based on which a mechanism was proposed and verified with experiments. On the whole, CuS can work as a multifunctional catalyst for promoting LOB performance, which means that the dissolved CuS in LiTFSI/TEGDME electrolyte can serve as a liquid catalyst by the redox couples of Cu(TFSI)2/Cu(TFSI)2-/Cu(TFSI)22-, in addition to the function as a traditional solid catalyst in the cathode.