Bifunctional electrolyte additive MgI₂ for improving cycle life in high-efficiency redox-mediated Li-O₂ batteries

Here, MgI₂ is introduced as a bifunctional self-defense redox mediator into dimethyl sulfoxide-based Li-O₂ batteries. During charging, I^- is first oxidized to I₃^-, which facilitates the decomposition of Li₂O₂, and thus reduces overpotential. In addition, Mg²⁺ spontaneously reacts with the Li anode to form a very stable SEI layer containing MgO, which can resist the synchronous attack by the soluble I₃^- and improve the interface stability between the Li anode and the electrolyte. Therefore, a Li-O₂ battery containing MgI₂ exhibits an extended cycling life span (400 cycles) and a quite low overpotential (0.6 V).