An analysis of the electrochemical mechanism of manganese oxides in aqueous zinc batteries

Because of their high energy density, safety, eco-friendliness, and sustainability, aqueous rechargeable zinc batteries (ARZBs) have attracted burgeoning interests. Manganese oxide cathodes are particularly attractive because they are obtained from earth-abundant and non-toxic materials. However, the diversity of mechanisms that explain the electrochemistry with Zn metal anodes in mildly acidic media hinders ARZBs’ further development. In brief, a specific manganese oxide polymorph, typically MnO₂, in mildly acidic electrolytes has been reported to exhibit different reaction mechanisms under similar electrochemical conditions. Moreover, the recently discussed dissolution/deposition process of MnO₂ in both strong and mildly acidic electrolyte media has revolutionized the conventional intercalation chemistry. To this end, this perspective aims to clarify and seek possible convergence of the conflicting electrochemical mechanisms for mildly acidic Zn-MnO₂ batteries. We also suggest future research directions and opportunities for commercialization that may evolve from the recently researched acid-alkaline Zn-MnO₂ battery technologies.