Surface Adsorption and Proton Chemistry of Ultra‐Stabilized Aqueous Zinc–Manganese Dioxide Batteries

Aqueous rechargeable Zinc (Zn) batteries incorporating MnO2 cathodes possess favorable sustainability properties and are being considered for low‐cost, high‐safety energy storage. However, unstable electrode structures and unclear charge storage mechanisms limit their development. Here, advanced transmission electron microscopy, electrochemical analysis, and theoretical calculations are utilized to study the working mechanisms of a Zn/MnO2 battery with a Co2+‐stabilized, tunnel‐structured α‐MnO2 cathode (CoxMnO2). It is shown that Co2+ can be pre‐intercalated into α‐MnO2 and occupy the (2 × 2) tunnel structure, which improves the structural stability of MnO2, facilitates the proton diffusion and Zn2+ adsorption on the MnO2 surface upon battery cycling. It is further revealed that for the MnO2 cathode, the charge storage reaction proceeds mainly by proton intercalation with the formation of α‐HyCoxMnO2, and that the anode design (with or without Zn metal) affects the surface adsorption of by‐product Zn4SO4(OH)6·nH2O on MnO2 surface. This work advances the fundamental understanding of rechargeable Zn batteries and also sheds light on efficient electrode modifications toward performance enhancement. A structural stability strategy is proposed to inhibit the dissolution of MnO2 in Zn‐based aqueous devices and provide atomic insights. Meanwhile, the storage mechanism of proton chemistry and Zn ion surface adsorption in CoxMnO2 is revealed. Moreover, the mechanism of the influence of the anode selection on the surface adsorption process is studied.