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.