Effect of Heat Treatment on the Crystallization Behavior of Amorphous Manganese Dioxide and its Electrochemical Properties in Zinc‐Ion Battery Cathodes

Herein, amorphous manganese dioxide (AMO) is prepared by the liquid‐phase coprecipitation method, the effect of heat treatment temperature on the microstructure, and phase composition of AMO and the electrochemical properties as cathode materials for aqueous Zn–MnO₂ batteries are investigated. The results show that the AMO didn't crystallize at 250 °C, but its structure stability increases. When the temperature is 350 and 400 °C, part of the AMO crystallizes into rod‐shaped nano‐α‐MnO₂ crystals. At 540 °C, the products crystallize into nano‐α‐MnO₂ crystals. Continuing to increase the temperature to 650 °C, the structural stability of the products is further improved. Heat treatment leads to reduced specific surface area and porosity of the material, which in turn leads to reduced specific capacity and cycling stability. In addition, the heat‐treated products show a sharp drop in capacity during the discharge process; this was because the volume change caused by the irreversible phase change of the electrode material is difficult to release in the anisotropic crystal, resulting in the collapse of the structure. This study shows that unheated AMO is better than heat‐treated AMO as a cathode material for aqueous Zn–MnO₂ battery cathode material in terms of overall performance and cost.