Partial Disproportionation Gallium-Oxygen Reaction Boosts Lithium-Oxygen Batteries

Abstract

Ex-situ catalysts have been used for Li-oxygen batteries (LOBs), mostly resulting in polycrystalline Li2O2 as the discharge product, whose high energy barrier for oxygen evolution impedes the extraction of full potential of LOBs. In this study, a partial disproportionation gallium-oxygen reaction of superoxide in (Ga2O2)2+2(O2−) is subtly created prior to the lithium-oxygen one, in-situ growing Ga2O3 nanoparticles at cathode. The Ga2O3 induce the formation of poorly crystalline Li2O2, opposite to the conventional polycrystalline one. Benefitting from the crystallinity and morphology transformations of Li2O2, the chemical oxidation reaction kinetics between iodide redox mediators (RMs) and Li2O2 is significantly enhanced. In this regard, some issues related to RMs, for instance, the well-known Li-I2 side reactions and shuttle effect between the residual I3− and Li anode, can be predominantly suppressed. As a result, the cyclability of the LOBs are significantly improved with stable electrical energy efficiency. Our results lead to two conclusions: (1) non-lithium metal-oxygen reaction with higher thermodynamic potential than lithium-oxygen one is corroborated by theoretical calculations, which can in-situ produce nano-sized metal oxides particles at cathode, functioning surface growth of poorly crystalline Li2O2, and (2) acceleration of the reaction kinetics between the Li2O2 and the oxidized state of RMs is experimentally confirmed, which creates a new solid-soluble mixed catalytic mechanism.