Unravelling the Mechanism of Rechargeable Aqueous Zn-MnO2Batteries: Implementation of Charging Process by Electrodeposition of MnO2

Poor cycling stability and mechanistic controversies have hindered the wider application of rechargeable aqueous Zn-MnO(2)batteries. Herein, direct evidence was provided of the importance of Mn(2+)in this type of battery by using a bespoke cell. Without pre-addition of Mn2+, the cell exhibited an abnormal discharge-charge profile, meaning it functioned as a primary battery. By adjusting the Mn(2+)content in the electrolyte, the cell recovered its charging ability through electrodeposition of MnO2. Additionally, a dynamic pH variation was observed during the discharge-charge process, with a precipitation of Zn-4(OH)(6)(SO4)5H(2)O buffering the pH of the electrolyte. Contrary to the conventional Zn(2+)intercalation mechanism, MnO(2)was first converted into MnOOH, which reverted to MnO(2)through disproportionation, resulting in the dissolution of Mn2+. The charging process occurred by the electrodeposition of MnO2, thus improving the reversibility through the availability of Mn(2+)ions in the solution.