Synthesis And Capacitive Behavior Evaluation Of Manganese Dioxide

As a new kind of energy storage devices between batteries and electrostatic capacitors, supercapacitors is characterized with excellent energy density, high power density, long life time and wide temperature range for using. So, the promising application of supercapacitor have been attracting more and more attention throughout the world. Studies on supercapacitor are mainly focused on the preparation of high performance electrode material and electrode. With cheaper MnO₂ as electrode materials for supercapacitor, by integrating various electrochemical and material methods, this dissertation has investigated the material preparation, characterization and factors affecting their capacitive properties. The main results are as follows:(1) Amorphous structure MnO₂ as electrode materials for supercapacitor was synthesized by the chemical precipitation method by mixing potassium permanganate and polyethylene glycol aqueous solution and the optimum preparation condition was determined by monofactorial study, which was confirmed to be 1:2(wt%), 60℃for temperature, and 2.5h for reaction time. The physical properties and electrochemical properties of the as-prepared electrode material were characterized by XRD, SEM, BET, FT-IR, redoxtitration, cyclic voltammetry and galvanostatic charging-discharging. The results showed that the as-synthesized powder had amorphous structure and spherical morphology. Its mean particle size and BET specific surface areas were of 100nm and 110.87m2/g, respectively. MnO₂ content reaches 83.75%. Within the potential window range from -0.6 to 0.4V(vs. SCE), this amorphous MnO₂ exhibited ideal capacitive behavior in 9mol/L KOH, which the maximum specific capacitance value of 420F/g were obtained at the 200mA/g,retained 180F/g after 500cycles.(2) MnO₂ as electrode materials for supercapacitor was synthesized by the hydrothermal method by mixing potassium permanganate and sodium dodecyl sulphate solution and the optimum preparation condition was determined by monofactorial study, which was confirmed to be 1:0.1(wt%), 130℃for temperature, and 20h for reaction time. The physical properties and electrochemical properties of the as-prepared electrode material were characterized by XRD, SEM, BET, FT-IR, redoxtitration, cyclic voltammetry and galvanostatic charging-discharging. The results showed that the powder was weak-crystallineα-MnO₂ with 100nm the mean particle size and 125.19m2/g BET specific surface areas. MnO₂ content reaches 87.23%. Within the potential window range from -0.6 to 0.4V(vs. SCE) the weak-crystallineα-MnO₂ exhibited excellent capacitive behavior in 9mol/L KOH, which the maximum specific capacitance value of 570F/g were obtained at the 200mA/g,retained 220F/g after 500cycles.(3) The effect about assembly method of MnO₂ electrochemical capacitors on their electrochemical capability has been researched systematically and the capability of electrochemical capacitor stack in series or in parallel configuration has been discussed.MnO₂ as electrode material was synthesized by the chemical precipitation method by mixing potassium permanganate and polyethylene glycol aqueous solution is a friendly method for environment, but its specific capacitance is only 180F/g. MnO₂ as electrode material for supercapacitor was synthesized by the hydrothermal method by mixing potassium permanganate and sulfuric acid aqueous solution. As a result of sulfuric acid as raw materials, it is not environmentally friendly method. Hydrothermal technique by mixing potassium permanganate and sodium dodecyl sulphate aqueous solution is a simple, cheap, environmentally friendly method to prepare MnO₂ electrode materials and the specific capacitance can reach 220F/g. This method may have great potential for industrial production.