Unveiling the Intricate Intercalation Mechanism in Manganese Sesquioxide as Positive Electrode in Aqueous Zn-Metal Battery

In the family of Zn/manganese oxide batteries with mild aqueous electrolytes, cubic alpha-Mn2O3 with bixbyite structure is rarely considered, because of the lack of the tunnel and/or layered structure that are usually believed to be indispensable for the incorporation of Zn ions. In this work, the charge storage mechanism of alpha-Mn2O3 is systematically and comprehensively investigated. It is demonstrated that the electrochemically induced irreversible phase transition from alpha-Mn2O3 to layered-typed L-ZnxMnO2, coupled with the dissolution of Mn2+ and OH- into the electrolyte, allows for the subsequent reversible de-/intercalation of Zn2+. Moreover, it is proven that alpha-Mn2O3 is not a host for H+. Instead, the MnO2 formed from L-ZnxMnO2 and the Mn2+ in the electrolyte upon the initial charge is the host for H+. Based on this electrode mechanism, combined with fabricating hierarchically structured mesoporous alpha-Mn2O3 microrod array material, an unprecedented rate capability with 103 mAh g(-1) at 5.0 A g(-1) as well as an appealing stability of 2000 cycles (at 2.0 A g(-1)) with a capacity decay of only approximate to 0.009% per-cycle are obtained.