Hydroxylated Manganese Oxide Cathode for Stable Aqueous Zinc-Ion Batteries

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-MnO2) is fabricated using an electrochemical method for stable aqueous Zn-Mn batteries without relying on the Mn2+ 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 Zn2+ adsorption thermodynamics and diffusion kinetics on the surface of H-MnO2 but weakens the interaction between H+ and the electrode. Therefore, Zn2+ ions can be more reactive with the hydroxylated manganese oxide than H+ ions. Experimental results show that the Zn2+ insertion mechanism dominates the charge storage process of H-MnO2, and the H+-induced Mn dissolution reaction is effectively alleviated. Importantly, H-MnO2 exhibits good cycling stability with 95% capacity retention over 5000 cycles at the current density of 3.8 A g-1 in the ZnSO4 electrolyte, outperforming the state-of-the-art aqueous Zn-Mn batteries, even those with Mn2+ electrolyte additives. The findings provide new insights for designing stable manganese oxide cathodes in aqueous Zn-Mn batteries. The H+-induced manganese (Mn) dissolution reaction in manganese oxide cathode for Zn-ion batteries is effectively mitigated via an electrochemical hydroxylation strategy. The hydroxylated manganese oxide with a high content of Mn-OH component exhibits good cycling stability over 5000 cycles, without relying on the commonly used Mn2+ additives. image