Enhancing Two-Electron Reaction Contribution in MnO2 Cathode Material by Structural Engineering for Stable Cycling in Aqueous Zn Batteries

MnO2 is a promising cathode for aqueous Znbatteries.However, the cycling stability is seriously hindered by active materialdissolution, and the pre-addition of Mn2+ salts in electrolytesis widely required. Herein, we propose a structural engineering strategyfor MnO2 to enhance the capacity contribution from thereversible two-electron transfer reaction of MnO2/Mn2+ and realize stable cycling in Mn2+-free electrolytes.By compositing with MoO3, MnO2 exhibits weakenedMn-O bonds, more oxygen vacancies, spontaneous generation ofstructural water, and thus a lowered energy barrier for Mn releaseduring discharge. Meanwhile, the composite material presents strongerelectrostatic attractions for dissolved Mn2+, which ensureshighly reversible re-deposition during charge. As a result, the massratios between materials undergoing reversible two-electron and one-electrontransfer reactions increase from 0.85 in MnO2 to 1.68 inthe MnO2/MoO3 composite material. In the ZnSO4 electrolyte, the MnO2/MoO3 cathodeachieves 92.6% capacity retention after 300 cycles at 0.1 A g(-1) (>1900 h), superior to 62.7% for MnO2.MnO2/MoO3 also retains 80.1% capacity after16 000 cycles at 1 A g(-1) (>3200 h). Thiswork presents an effective path to realize stable cycling of MnO2 in Zn batteries.

Automated summary

Researchers proposed a structural engineering strategy to enhance the capacity contribution of MnO2 in aqueous Zn batteries, achieving stable cycling in Mn2+-free electrolytes. By compositing with MoO3, the MnO2/MoO3 cathode showed improved stability and capacity retention in ZnSO4 electrolyte. The mass ratios between materials undergoing reversible two-electron and one-electron transfer reactions significantly increased in the MnO2/MoO3 composite material compared to pure MnO2.