Chemical Mediation Mechanism Decouples Solid State Kinetics for High‐Power Aqueous Zn‐Co Batteries

Abstract

ABSTRACT Solid state conversion electrodes are promising for aqueous energy storage but are frequently constrained by sluggish interfacial kinetics, leading to a persistent energy‐power trade‐off and underutilized capacity at high rates. Here we propose a chemical mediation strategy in which dissolved [Fe(CN) 6 ] 4− /[Fe(CN) 6 ] 3− couples continuously regenerate an interfacial oxidant to chemically drive the α‐Co(OH) 2 to CoOOH conversion, thereby rewriting the rate limiting solid state electrochemical step into an electrochemical‐chemical cascade at the electrode/electrolyte interface. Electrochemical analyses and spectroscopy corroborate the spontaneous oxidative phase transformation and the mediator enabled pathway reconstruction beyond simple solid–liquid capacity superposition. To make this capacity boosting strategy practically efficient, we further tune the initial redox composition of the mediator couple to suppress shuttle driven self‐discharge while maintaining fast interfacial conversion kinetics, as quantified by multi‐potential‐step measurement (MPSM) and visualized by in situ Raman mapping. Consequently, the redox‐enhanced alkaline Zn‐Co battery exhibits a remarkable areal capacity of 0.98 mAh cm −2 (a 96% enhancement), while simultaneously retaining a high energy density of 0.92 mWh cm −2 and an ultrahigh‐power density of 75 mW cm −2 . This work highlights a functional electrolyte design route to unlock deep solid state conversion capacity under high‐power operation in aqueous batteries.