Charge–Discharge Performances and Mechanisms of Zn-Ion Batteries with β-MnO2, γ-MnO2, and Mn2O3 Positive Electrodes

Abstract

In the present study, the charge–discharge characteristics of zinc-ion batteries fabricated with β-MnO2, γ-MnO2, or Mn2O3 as the positive-electrode material were evaluated. MnOOH is widely believed to be formed in the discharge reaction of γ-MnO2. However, when β-MnO2 was used as the positive-electrode material, we observed the formation of Mn2O3 and Mn3O4 instead of MnOOH in the first discharge reaction, and no reformation of β-MnO2 upon charging occurred. Furthermore, during the charge–discharge process, zinc was dissolved from the negative electrode, and basic zinc compounds were observed as byproducts at both the positive and negative electrodes. For the second cycle onwards, the amounts of Mn2O3 and Mn3O4 increased during discharging and decreased during charging. The process showed a stable discharge capacity of 200 Ahkg−1 until ∼30 cycles, thereafter decreasing to 105 Ahkg–1 by the 100th cycle.