Potassium-Ion-Doped Manganese Oxides and Kaolinite Electrolyte Additives for Aqueous Zinc-Ion Batteries

Abstract

Manganese oxide is considered as a cathode material with great application potential for zinc-ion batteries (ZIBs). However, the dissolution, low electrical conductivity, and slow ion diffusion rate of manganese oxide are the main limiting factors to its rate capacity and cycle stability. Here, K-doped α-MnO2 nanowires were employed as cathode materials for ZIBs in conjunction with kaolinite (KL) as an electrolyte additive. The combination of ion doping and the KL electrolyte additive made the batteries exhibit remarkable zinc energy storage properties, including an improved capacity of 226 mAh g–1, excellent cycle stability with a capacity retention rate of 99.5% at 0.5 A g–1 after 270 cycles, and improved rate performances. The expansion of the tunnel structure spacing in supported α-MnO2 induced by K+ intercalation intentionally creates additional space for the efficient transportation of H+/Zn2+ ions during the discharge/charge process. The KL electrolyte additive improves the ion conductivity of the battery. The evolution of diffraction peaks and morphological changes of 5ZHS, 0.5ZHS, ZnMn2O4, and MnOOH during the discharge/charge process demonstrate the cointercalation of the H+/Zn2+ mechanism.