Activating the redox chemistry of MnO₂/Mn²⁺ in aqueous Zn batteries based on multi-ions doping regulation

Two electron reaction of MnO₂/Mn²⁺ have attracted burgeoning attention, which endows rechargeable aqueous Zn-MnO₂ batteries with high energy density besides intrinsic safety, and environmental friendliness. However, it also suffers uncontrolled anode corrosion, sluggish ion diffusion and irreversible structural transformation, leading to poor rate capability and severe fading. Herein, a multi-ions regulated MnO₂ (CrNi-MnO₂) is designed via a novel two-step electrochemical method under theoretical guidance, contributing to the enhanced electrochemical performance of Zn-MnO₂ batteries in terms of dissolution-deposition chemistry. CrNi-MnO₂ cathode can significantly improve the conductivity and lower electrostatic interaction, boosting the rate performance and cycling stability. Furthermore, reversible Cr³⁺/Cr²⁺ reaction can effectively reduce the accumulation of “dead” MnO₂, which can promote the transformation of MnO₂/Mn²⁺ thoroughly in acid-mild electrolyte. Various ex-situ analyses and theory calculations have revealed double-functional role of the doped ions for accelerating MnO₂/Mn²⁺ transformation and Zn²⁺/H⁺ co-insertion kinetics. Hence, CrNi-MnO₂ cathode exhibits ultra-high capacity, superior rate performance, and excellent cycling stability, providing new insight for developing superb Zn-MnO₂ batteries.