Interface-Controlled Redox Chemistry in Aqueous Mn⁺/MnO₂ Batteries.

Manganese dioxide (MnO) deposition/dissolution (Mn/MnO) chemistry, involving a two-electron-transfer process, holds promise for safe and eco-friendly large-scale energy storage. However, challenges like electrode/electrolyte interface environment fluctuations (H and HO activity), irreversible Mn degradation, and limited understanding of degradation mechanisms hinder the reversibility of the Mn/MnO conversion. This study demonstrates a vanadyl/pervanadyl (VO/VO ) redox-mediated interface designed for high-energy Mn/MnO batteries. Unlike flow systems, this work uncovers, for the first time, the mechanism of a static redox-mediated interface in regulating interfacial H and HO activities. Significantly, the VO/VO chemical redox mediation targets Mn intermediates, suppressing their hydrolysis and enabling 100% Mn/MnO conversion. The redox-mediated interface enhances the Mn redox electron transfer process, achieving a stable ≈95% coulombic efficiency and ultrahigh capacity of 100 mAh cm with an areal energy density of 111 mWh cm , outperforming flow systems. The electrode also exhibits an average specific capacity of 593 mAh g, approaching the theoretical limit of 616 mAh g, and a specific energy density of 721 Wh kg at high MnO loadings (50-150 mg cm). The findings highlight the critical role of interfacial redox mediation in regulating H and HO activities and underscore the significance of interface dynamics.