Charge–Discharge Performances and Mechanisms of Zn-Ion Batteries with β-MnO 2 , γ-MnO 2 , and Mn 2 O 3 Positive Electrodes

Abstract

In the present study, the charge–discharge characteristics of zinc-ion batteries fabricated with β -MnO 2, γ -MnO 2 , or Mn 2 O 3 as the positive-electrode material were evaluated. MnOOH is widely believed to be formed in the discharge reaction of γ -MnO 2 . However, when β -MnO 2 was used as the positive-electrode material, we observed the formation of Mn 2 O 3 and Mn 3 O 4 instead of MnOOH in the first discharge reaction, and no reformation of β -MnO 2 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 Mn 2 O 3 and Mn 3 O 4 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.