Influence of Thermal Decomposed Temperatures on the Capacity Behaviors of Manganese Dioxides

Manganese dioxides were prepared by direct thermal decomposition of KMnO4 at different temperatures. XRD and TEM measurements show that the materials contain a large amorphous/ crystalline ratio and have layered structures with K+ ions between them. Cyclic voltammetry tests indicate that the materials prove to be excellent electrodes for electrochemical capacitors in a mild 0.5mol/L Na2SO4 aqueous electrolyte. A sample decomposed at 550℃ gives a specific capacitance of 243F·g-1 between -0.2 and +1.0V(vs. SCE), and an excellent cyclability after 200 cycles at constant current 40mA and its specific capacitance remains over 95%.