Hydroxylated Manganese Oxide Cathode for Stable Aqueous Zinc‐Ion Batteries

Abstract Manganese (Mn) oxides are promising cathode materials for rechargeable aqueous Zn‐ion batteries. However, the Mn dissolution in weakly acidic electrolytes always hinders the development of better aqueous Zn–Mn batteries. Herein, a hydroxylated manganese oxide cathode material (H‐MnO 2 ) is fabricated using an electrochemical method for stable aqueous Zn–Mn batteries without relying on the Mn 2+ electrolyte additives. The partial hydroxylation of the oxides leads to charge redistribution of the material, changing the reaction thermodynamics and kinetics. Theoretical simulation suggests that the hydroxylation of manganese oxide promotes both Zn 2+ adsorption thermodynamics and diffusion kinetics on the surface of H‐MnO 2 but weakens the interaction between H + and the electrode. Therefore, Zn 2+ ions can be more reactive with the hydroxylated manganese oxide than H + ions. Experimental results show that the Zn 2+ insertion mechanism dominates the charge storage process of H‐MnO 2, and the H + ‐induced Mn dissolution reaction is effectively alleviated. Importantly, H‐MnO 2 exhibits good cycling stability with 95% capacity retention over 5000 cycles at the current density of 3.8 A g −1 in the ZnSO 4 electrolyte, outperforming the state‐of‐the‐art aqueous Zn–Mn batteries, even those with Mn 2+ electrolyte additives. The findings provide new insights for designing stable manganese oxide cathodes in aqueous Zn–Mn batteries.