A self-defense redox mediator for efficient lithium-O₂ batteries

Redox mediators (RMs) have become focal points in rechargeable Li-O₂ battery research to reduce overpotentials in oxygen evolution (charge) reactions. In this study, we found an evidence for the shuttle effect arising in dimethyl sulfoxide (DMSO) with a LiI RM through the visual observation of the diffusion of soluble I₃^- towards a Li anode where it reacted chemically to produce LiI, which can be only partly dissolved, leading to the loss of both the RM and electrical energy efficiency. Therefore, we proposed a self-defense redox mediator (SDRM) of InI₃ to counter this problem. During charging, the In³⁺ is reduced electrochemically on the Li anode prior to Li⁺, forming a much stable indium layer to resist the synchronous attack by the soluble I₃^-. The pre-deposited indium layer can also reduce the growth of dendrites from the Li anode surface. As a result, the electrical energy efficiency and the cycling performance of the Li-O₂ cells were improved significantly.