Studies Of Supercapacitors Based On Manganese Oxides And Carbon Materials

Supercapacitors have been recognized as unique energy storage devices which have higher energy density than conventional capacitors, and higher power density and longer cycle life than batteries, filling the gap between conventional dielectric capacitors and batteries. They can release huge discharge current instantly. Based on the above, the promising application of supercapacitors in the fields such as mobile telecommunication, information technology, consumer electronics, electric vehicle, aviation & aerospace, and military force, have been attracting more and more attention throughout the world. Studies on supercapacitors are mainly focused on the preparation of high performance electrode material and electrode. With conductive carbon black with high specific surface area, activated carbon and cheaper manganese oxide as electrode materials for supercapacitors, by integrating various electrochemical and material methods, this dissertation has investigated the material preparation, electrolyte optimization, electrode preparation, capacitive property and mechanism of pseudocapacitance. The main results are as follows:1. For the first time, the industrial conductive carbon black with high specific surface area has been used as electrode material for supercapacitor. By investigating electrode preparation and capacitor assembly technology, using cyclic voltammogram and constant current charge/discharge methods, capacitive characteristics of carbon black supercapacitor are studied. The results show that the carbon black (CB) is a good electrode material for supercapacitor, which exhibits typical double-layer capacitive behavior, high reversibility, low equivalent serial resistance (ESR) and high power property. The specific capacitance of CB is 60~70 F/g. Activated carbon/ carbon black (AC/CB) composite electrode materials are prepared by utilizing ultrasonic mixing technology. By optimizing the AC/CB ratio, the specific capacitance of the composite electrode is maximized when the mass ratio of AC/CB is 7:2; the discharge specific capacitance is 133.6 F/g and 110 F/g in KOH andelectrolyte at 5 mA respectively; the discharge specific capacitance declines while increasing the discharge current.2. MnC>2 as electrode material for supercapacitor is synthesized by chemical coprecipitation method. The effects of heat treatment, discharge current and cycle number on the capacitive characteristics of the manganese oxides are investigated. MnO2 prepared by low temperature treatment shows typical capacitive behavior with the potential windows from -0.2 to +0.8 V(vs SCE) in 1 mol/L Na2SC>4 neutral aqueous electrolyte. Amorphous hydrous nanostructured MnC>2, with the mean particle size of 10-30 nm, the pore size distribution in the range of 1-15 nm, and BET specific surface area of 160.7 m2/g, is synthesized by chemical coprecipitation method by mixing KMnO4 and manganese acetate aqueous solution using polyethylene glycol (PEG) as disperser. The specific capacitance of 203.4 F/g is obtained at the scan rate of 4 mV/s. The manganese oxide electrodes are prepared by ultrasonic mixing technology and mechanical mixing technology. The results show that the manganese oxide electrodes by ultrasonic mixing technology exhibit good power properties by cyclic voltammetry. Effects of composition and concentration on capacitive characteristics of hydrous nanostructured MnC>2 are investigated. Capacitance mechanism of manganese oxide electrode in neutral electrolyte is also discussed.3. The MnO2 /CB nanocomposite materials are synthesized by simple chemical coprecipitation using PEG and Polyvinylpyrrolidone (PVP) as surfactant dispersers. Under the conditions of different potential windows, different scan rates and different current charge/discharge, effects on MnCVCB nanocompostie electrode are studied by cyclic voltammetry (CV) and constant current charge/discharge methods. The amorphous nanocomposite electrode material in 1 mol/L Na2SO4 aqueous electrolyte exhibits ideal capacitive behavior, high reversibility and high pulse charge-discharge property indicating a promising electrode material for supercapacitor. Specific capacitance of the composite as high as 142.02 F/g is obtained in the range of -0.2-+0.8 V(vs SCE). Button supercapacitor cells are successfully prepared...