Unravelling the Mechanism of Rechargeable Aqueous Zn–MnO(2) Batteries: Implementation of Charging Process by Electrodeposition of MnO(2)

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 Mn(2+), 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 MnO(2). Additionally, a dynamic pH variation was observed during the discharge–charge process, with a precipitation of Zn(4)(OH)(6)(SO(4))⋅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 Mn(2+). The charging process occurred by the electrodeposition of MnO(2), thus improving the reversibility through the availability of Mn(2+) ions in the solution.