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

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