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

The reaction chemistry and degradation mechanism of MnO2-based cathodes remain controversial, which hinder their applications in energy storage. Herein, a conversion reaction between Zn4SO4 center dot(OH)(6)center dot nH(2)O (ZSH) and ZnxMnO(OH)(2) (ZMO) is proposed in ZnSO4-based electrolytes. The conversion reaction is an important component of the reaction chemistry as well as the Zn2+/H+ intercalation/deintercalation reaction, which not only provides electrochemical capacity but also dominates the degradation of MnO2 cathodes. The massive accumulation of inactive ZMO seriously destroying the dynamic performance of MnO2 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 MnO2 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 MnO2 cathode equipped with the activated conversion reaction. Impressively, the conversion reaction activated by voltage modulation is applicable to various crystal forms of MnO2 (alpha-, beta-, gamma-, delta-), which is significant for the ZIBs with a long lifespan.