Crystallization Behavior of Co-Doped Amorphous Manganese Dioxide and Its Cathode Performance for Aqueous Zinc Ion Batteries

Abstract

In order to explore the crystallization behavior of Co-doped amorphous manganese dioxide(Co-doped AMO) and to investigate the electrochemical properties of its different crystallization products as cathodes for aqueous zinc ion batteries. In this work, the effects of heat treatment temperature on the microstructure and phase composition of Co-doped AMO and their electrochemical properties of Zn-MnO₂ battery cathode materials are systematically investigated. The results show that Co-doping increases the crystallization temperature of pure AMO. When the heat treatment temperature is 400 °C, Co-doped AMO is amorphous. At 500 and 550 °C, part of the Co-doped AMO crystallizes into tetragonal spinel structured (Co, Mn)(Co, Mn)₂O₄ material between MnCo₂O₄ and Mn₃O₄. At 650 °C, the crystallized product is completely nano-α-Mn(Co)O₂ crystal. The maximum discharge specific capacities and the retention rate after 100 cycles of the samples at 100 mA g⁻¹ are 325.40 mAh g⁻¹, 86.88%; 217.00 mAh g⁻¹, 13.94%; 186.68 mAh g⁻¹, 41.01%; and 149.03 mAh g⁻¹, 31.27% for the unheated and 400, 550, 650 °C heat-treated samples, respectively. It is proved that the Co-doped AMO without heat treatment is superior to the partially or fully crystallized materials in terms of comprehensive performance and cost as cathode materials for AZIB.