Vanadium(III) Acetylacetonate as an Efficient Soluble Catalyst for Lithium-Oxygen Batteries.

High donor number (DN) solvents in Li-O2 batteries that dissolve superoxide intermediates in lithium peroxide (Li2 O2 ) formation facilitate high capacities at high rates and avoid early cell death. However, their beneficial characteristics also result in an instability towards highly reactive superoxide intermediates. Furthermore, Li-O2 batteries would deliver a superior energy density, but the multiphase electrochemical reactions are difficult to achieve when operating with only solid catalysts. Herein we demonstrate that vanadium(III) acetylacetonate (V(acac)3 ) is an efficient soluble catalyst that can address these problems. During discharge, V(acac)3 integrates with the superoxide intermediate, accelerating O2 reduction kinetics and reducing side reactions. During charge, V(acac)3 acts as a redox mediator that permits efficient oxidation of Li2 O2 . The cells with V(acac)3 exhibit low overpotential, high rate performance, and considerable cycle stability.