Enriching Oxygen Vacancy Defects via Ag–O–Mn Bonds for Enhanced Diffusion Kinetics of δ-MnO2 in Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) have received great attention due to their environmental friendliness and high safety. However, cathode materials with slow diffusion dynamics and dissolution in aqueous electrolytes hindered their further application. To address these issues, in this work, a MnO2-2 cathode doped with 1.12 wt % Ag was prepared, and after 1000 cycles of charge/discharge at 1 A·g-1, the capacity remained at 114 mA·h·g-1 (only 57.7 mA·h·g-1 for pristine MnO2). Cyclic voltammetry (CV), the galvanostatic intermittent titration technique (GITT), the electrochemical quartz crystal microbalance (EQCM) method, and density functional theory (DFT) calculation on pristine δ-MnO2 and MnO2-2 also proved the superior performance of MnO2-2. More investigation disclosed that its superior performance is attributed to the improved diffusion kinetics of the cathode brought by the enriched oxygen vacancy defects due to the formation of Ag-O-Mn bonds. Meanwhile, the kinetic mechanism of the Zn/MnO2-2 cell can be described as a reversible process of the dissolution/precipitation of the ZHS phase and consequent insertion/extraction of Zn2+ and H3O+. Herein, the primary issues of ZIB cathode materials have been addressed and solved to a certain extent. More importantly, such a modification in the design of the advanced manganese-based aqueous ZIB cathode materials can provide further insight and facilitate the development and application of this large-scale energy storage system in the near future.