Batch Synthesis of K-Doped α-MnO2 Nanorods as Cathode Materials for Aqueous Zinc-Ion Battery

MnO2 is widely used as the cathode material for aqueous zinc-ion batteries because of its tunnel structure, which is suitable for zinc storage. Nevertheless, MnO2 faces issues such as inherent poor conductivity, slow ion diffusion kinetics, and structural collapse due to the manganese dissolution during cycling, resulting in significant degradation of electrochemical performance. In addition, current synthesis methods of MnO2 often involve high costs and complex operations. Therefore, a gentle method for batch synthesis of K-doped α-MnO2 (KMO) nanorods is proposed in this study, and the chemical conversion reactions between H+, Zn2+, and MnO2 are revealed by in situ X-ray diffraction (XRD) and density functional theory (DFT) calculations. The specific capacity of the KMO nanorods at 0.2 A g–1 is 218.1 mA h g–1. After 130 cycles, the capacity retention is still 100%. Even at 1.0 A g–1, the capacity of 99.6 mA h g–1 can be maintained after 1400 cycles, revealing the excellent cycling stability and long cycle life of the KMO nanorods.