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Transition metal layered double hydroxides (LDHs) are widely used as high‐performance cathode materials for aqueous alkaline zinc (Zn) batteries. Yet, the strongly alkaline electrolytes may lead to undesirable rechargeability of the alkaline devices and environmental issues. Herein, as a research prototype, CoNi LDH material is designed with abundant H vacancies using electrochemical methods (denoted as CoNi LDH(v)). As a Zn‐ion battery cathode, CoNi LDH(v) exhibits promising electrochemical performances in mild ZnSO4 electrolyte, such as a good specific capacity of 185 mAh g−1 at the current density of 1.2 A g−1, a high average discharge potential of 1.6 V versus Zn2+/Zn, and a large energy density of 296.2 Wh kg−1 at the power density of 1894 W kg−1, outperforming most of the cathode materials for aqueous Zn‐ion batteries. Experimental and computational results indicate that the introduced H vacancies in the double hydroxide matrix induce the improved electronic conductivity and cation adsorption thermodynamics, endowing the double hydroxides with good electrochemical activity for reversible cation insertion. Structural and spectroscopy studies identify that CoNi LDH(v) experiences reversible H+/Zn2+ co‐intercalation mechanism in an aqueous ZnSO4 electrolyte. As far as it is known, it is the first report on transition‐metal‐based double hydroxides used for mild aqueous Zn‐ion batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reversible MnO 2 /Mn2+ transformation is realized in mild aqueous electrolytes. • The Zn-Mn hybrid battery exhibit high discharge capacity and long cycle life. • The disproportionation of Mn3+ triggers the Mn2+ dissolution. • H+/Zn2+ insertion and the disproportionation occur sequentially upon discharging. The disproportionation of the Jahn-Teller (J-T) active manganese oxides (Mn3+) often leads to uncontrollable Mn2+ dissolution, which has been identified as one of the major causes of the performance degradation in conventional Zn-MnO 2 batteries. Herein, we use the "unwanted" disproportionation of the Mn3+ cations to realize effective MnO 2 /Mn2+ transformation, achieving high specific capacity (550 mAh g−1) and good cycling stability (5000 cycles without capacity decay) in a Zn-MnO 2 hybrid battery with mild aqueous electrolytes. Mechanism study shows that MnO 2 is deposited on the cathode during charging, H+/Zn2+ insertion and disproportionation occur sequentially during discharging, leading to Mn2+ dissolution. The generated high-valence manganese oxides via disproportionation further experience reduction-disproportionation-dissolution, which proceeds repeatedly in the expanded discharge potential to 0 V vs. Zn2+/Zn, resulting in the complete dissolution of the cathodic materials. Our results provide the fundamental understanding on the controversial mechanisms of Zn-MnO 2 batteries with mild aqueous electrolytes and highlight the effect of disproportionation in pushing the electrochemical performance of the promising Zn-MnO 2 hybrid batteries. [ABSTRACT FROM AUTHOR]