Modulating the Proton-Conducting Lanes in Spinel ZnMn_2O_4 through Off-Stoichiometry

摘要

The intercalation of protons represents a notable component for energystorage in aqueous zinc-ion batteries. However, the mechanism of protontransport in metal oxide cathodes, especially related to how the cation distributionmodulates the proton-conducting lanes, remains far from consensusdue to the lack of suitable model materials. Here, taking spinel ZnMn_2O_4cathode as a prototype, it is disclosed that a deficiency of one half of latticeZn ions can triple its specific capacity at high rates, which is predominantlycontributed by proton storage. This promotion can be rationalized by theemergence of facile concerted proton transport in the Zn-deficient sample,contrasting with the stoichiometric one, where proton intercalation undergoesa slow consecutive process. Furthermore, the restricted Zn motion inspinel phase causes high structural stability during cycling, preventing therecombination of external Zn ions with Zn vacant sites that readily accommodateprotons. This work highlights the key role of controlled off-stoichiometryin optimizing proton transport and storage for aqueous batteries.