Unconventional Copper Electrochemistry in Aqueous Zn‖CuMn2O4 Batteries

Abstract Manganese oxide is among the most promising cathode materials for rechargeable aqueous zinc‐ion batteries due to its abundant reserves, low toxicity, and high theoretical capacity. However, the occurrence of Mn dissolution and structural collapse during the charge and discharge process, as well as the hydrogen evolution reaction, zinc dendrite formation, and corrosion on the anode surface, have seriously hindered practical applications. Here, a novel cathode material design is proposed intended to enhance both cathode and anode stability simultaneously. Specifically, an inherently stable CuMn 2 O 4 is employed as cathode material, which demonstrates good maintenance of its spinel structure during cycling. Interestingly, insertion of Zn 2+ ‐ions leads to the extraction of Cu 2+ ‐ions from CuMn 2 O 4 , subsequently in situ reduces to Cu 0 , which results in extra capacity and improves electrical conductivity. The migration of Cu 2+ ions into the Zn anode surface during the charge process eventuated the formation of copper–zinc alloys via electrodeposition. Moreover, the reconstructed anode exhibits superior stability and corrosion resistance during the Zn plating‐stripping process. Consequently, the CuMn 2 O 4 electrode demonstrates a markedly improved cycle capability compared to the spinel Mn 3 O 4 electrode. This study highlights an unconventional copper electrochemistry in aqueous Zn‐Mn batteries and introduces a new design principle for high‐performance aqueous zinc‐ion batteries.