Thermal Treatment Effects on Manganese Dioxide Structure, Morphology and Electrochemical Performance

Abstract

Kinetic analysis is used to determine the required isothermal heating time at various temperatures to theoretically completely remove water from an electrolytic manganese dioxide (EMD) sample. The effect of the heat treatment regime on material structure, morphology and composition is investigated using various physical techniques, including X-ray diffraction and gas adsorption. Further, the electrochemical performance of heat treated EMD (HEMD) samples at a range of discharge rates finds that material properties such as retention of the γ-MnO2 structure and high surface area for the sample heat treated at 250°C, and extensive structural conversion and micro-pore closure in the case of the 350°C material, lead to higher capacity and power output. Conversely, significant amounts of structural water in the 200°C sample, and the compromise in structural rearrangement and surface area loss for the material prepared at 300°C, result in poor electrochemical behaviour, especially at high discharge rates. Particularly evident from this study is the complex interplay between the heat treatment regime, resulting HEMD properties and electrochemical performance.