Manganese(ii) oxide-embedded dopamine-derived carbon nanospheres for durable zinc-ion batteries†

Manganese oxides are considered highly promising as cathode materials for aqueous zinc-ion batteries (ZIBs) owing to their abundant resources, high discharge potential, and substantial theoretical capacity. Nonetheless, MnO is commonly perceived to exhibit insufficient electrochemical activity and is deemed unsuitable for Zn²⁺ storage. Herein, MnO-embedded PDA-derived carbon (MnO/C-PDA) is utilized as the cathode material for ZIBs, and its electrochemical behavior in ZnSO₄ electrolytes with varying MnSO₄ concentrations is investigated. The results indicate that the incorporation of manganese salt electrolyte notably enhances electrode capacity, though excessively high concentrations of manganese salt diminish electrode activity. In the electrolyte containing 0.2 M MnSO₄, MnO-C/PDA exhibits a capacity of 295.4 mA h g⁻¹ at 0.1 A g⁻¹, with negligible capacity degradation even after 100 cycles. Ex situ characterization reveals that during the charging process, MnO transformed into amorphous MnO_x, accompanied by the deposition of manganese salts forming MnO_x, while the discharge process involved the co-insertion of Zn²⁺ and H⁺. This work is anticipated to enhance comprehension regarding the charge and discharge mechanisms of MnO, thus aiding in the development of manganese oxide cathodes tailored for ZIBs.