The role of Cu ions of the self-reassembled MnO2 nanosheets for rechargeable aqueous batteries

Cu2+ ions inserted MnO2 electrodes (Cu-NS-MnO2) were prepared via nanosheet processes, and their electrochemical properties were investigated. In basic aqueous solutions, layer-structured MnO2 compounds usually show the irreversible phase transformation into Mn3O4 phase with a rapid decrease in a capacity. In this study, however, the Cu-NS-MnO2 showed relatively good cyclic properties with slow phase transformation at KOH solution. The Cu-NS-MnO2 exhibited a large discharge capacity of 230 mAh/g-MnO2 at the first cycle, and maintained a specific capacity of 170 mAh/g-MnO2 after 10 cycles at a current density of 300 mA/g-MnO2. These results suggest that Cu ions and nanosheet processes have effects to inhibit the irreversible phase transformation into Mn3O4 phase and maintain electrochemical activity under the basic condition. In this study, the role of Cu ions on electrochemical properties of the self-reassembled MnO2 nanosheets was investigated.