High-Voltage Manganese Oxide Cathode with Two-Electron Transfer Enabled by a Phosphate Proton Reservoir for Aqueous Zinc Batteries

MnO2cathodes typically undergo one-electron transfer in aqueouszinc batteries. The two-electron MnO2/Mn2+reaction provides double capacityand higher voltage. However, this requires a highly acidic environment, whichchallenges the Zn metal anode. Herein, we present a proton reservoir for theMnO2/Mn2+reaction. Zinc hydrophosphate is codeposited with MnO2at thecathode. The former deprotonates to release protons and enhances the reductionof MnO2to Mn2+. The resulting zinc phosphate further interacts with MnO2andrealizes spontaneous water desorption from the MnO2surface as revealed bytheoretical calculations, which facilitates the dissolution process. The hydro-phosphate species is reversibly generated upon charge. Based on this reactionmechanism, the cathode achieves a high discharge voltage of 1.75 V. It alsodelivers 0.99 mAh cm-2capacity with 99% Coulombic efficiency. Stable capacityretention is realized for over 3000 cycles. This work demonstrates an effectivestrategy to access the two-electron process of MnO2cathode materials in aqueous zinc batteries

Automated summary

In aqueous zinc batteries, the two-electron process of MnO2 cathode materials is achieved by co-deposition with zinc hydrophosphate, leading to increased capacity and voltage. The zinc hydrophosphate releases protons to enhance the reduction and dissolution of MnO2, as confirmed by theoretical calculations and experimental results.