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, which can 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.

Key words: Aqueous rechargeable battery, Manganese dioxide, Electrolyte, Zinc and manganese ion storage