Conversion Reaction of the Zinc Sulfate Hydroxide Activated by Voltage Modulation for High‐Performance Aqueous Zn/MnO2 Batteries

Abstract The reaction chemistry and degradation mechanism of MnO 2 ‐based cathodes remain controversial, which hinder their applications in energy storage. Herein, a conversion reaction between Zn 4 SO 4 ·(OH) 6 · n H 2 O (ZSH) and Zn x MnO(OH) 2 (ZMO) is proposed in ZnSO 4 ‐based electrolytes. The conversion reaction is an important component of the reaction chemistry as well as the Zn 2+ /H + intercalation/deintercalation reaction, which not only provides electrochemical capacity but also dominates the degradation of MnO 2 cathodes. The massive accumulation of inactive ZMO seriously destroying the dynamic performance of MnO 2 cathodes is deemed to be a principal trigger of the degradation mechanism. Intriguingly, the conversion reaction is sensitive to voltage, which can be activated by voltage modulation. Active ZMO generated in the activated conversion reaction is endowed with higher reversibility and electrooxidation, avoiding the accumulation of inactive ZMO and the decline of kinetic performance, which are evidenced by MnO 2 and ZSH cathodes. Accordingly, superior cycling stability with a capacity retention of 89.1% after 2000 cycles is achieved at 2 A g −1 for the MnO 2 cathode equipped with the activated conversion reaction. Impressively, the conversion reaction activated by voltage modulation is applicable to various crystal forms of MnO 2 ( α ‐, β ‐, γ ‐, δ ‐), which is significant for the ZIBs with a long lifespan.