Dissolution–Redeposition\nMechanism of the MnO₂ Cathode in Aqueous Zinc-Ion Batteries

Abstract

A dissolution–redeposition\nreaction mechanism of the MnO₂ cathode is directly visualized\nin rechargeable aqueous zinc-ion\nbatteries via <i>in situ</i> Raman microscopy. MnO₂ is reduced to Mn³⁺ during the discharge process, followed\nby a disproportionation reaction to form Mn²⁺ and Mn⁴⁺. The dissolved Mn²⁺ plays an important role in\nthe battery chemistry. During the following charge process, the redeposition\nof Mn²⁺ forms a species with high Zn-content on the surface\nof the MnO₂ cathode in the high-potential window. Moreover,\nan effective method that allows <i>in operando</i> observation\nof Jahn–Teller distortion of manganese is provided for the\nfirst time. This method uses <i>in situ</i> Raman microscopy\nto reveal the correlation between Jahn–Teller distortion and\nMn–O bond length change.