Enhanced cycle stability of aprotic Li-O2batteries based on a self-defensed redox mediator

LiBr as a promising redox mediator (RM) has been applied in Li-O2batteries to improve oxygen evolution reaction kinetics and reduce overpotentials. However, the redox shuttle of Br3−can induce the unexpected reactions and thus cause the degradation of LiBr and the corrosion of Li anode, resulting in the poor cyclability and the low round-trip efficiency. Herein, MgBr2is firstly employed with dual functions for Li-O2batteries, which can serve as a RM and a SEI film-forming agent. The Br–is beneficial to facilitating the decomposition of Li2O2and thus decreasing the overpotential. Additionally, a uniform SEI film containing Mg and MgO generates on Li anode surface by the in-situspontaneous reactions of Mg2+and Li anode in an O2environment, which can suppress the redox shuttle of Br3−and improve the interface stability of Li anode and electrolyte. Benefiting from these advantages, the cycle life of Li-O2battery with MgBr2electrolyte is significantly extended.