Effect of electrolyte on the electrochemical performance of the MnO2 cathode for aqueous rechargeable batteries

Abstract

The effect of Li+, Zn2+, and Mn2+ ions in aqueous solution on the electrochemical performance of the MnO2 cathode characterized by different crystal structures and morphologies was investigated. The energy storage mechanism of MnO2 in the mixed solution was probed. The results show that in aqueous solution without Mn2+ ions, various MnO2 electrodes exhibit similar electrochemical performance with low capacity and severe attenuation. In an aqueous solution with Zn2+ ions, the capacity of MnO2 electrodes is enhanced, whichcan be attributed to insertion/extraction of zinc ions. However, the decay of the capacity is drastic. When aqueous solutions containing Mn2+ and Zn2+ ions are used, particle aggregation and crystal structure collapse of MnO2 are effectively prevented owing to the synergistic effect of zinc and manganese ions and the redox reaction process of Mn2+ ions. The negative influence of the ZnSO4∙3Zn(OH)2 impurity is also weakened. As a result, the high capacity of MnO2 electrodes resulting from insertion/extraction of zinc ions is maintained (~200 mAh∙g-1 at 100 mA∙g-1) with excellent cycling stability.