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

Abstract

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).