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

High donor number (DN) solvents in Li-O-2 batteries that dissolve superoxide intermediates in lithium peroxide (Li2O2) 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-O-2 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 O-2 reduction kinetics and reducing side reactions. During charge, V(acac)(3) acts as a redox mediator that permits efficient oxidation of Li2O2. The cells with V(acac)(3) exhibit low overpotential, high rate performance, and considerable cycle stability.