Research On The Electrode Materials And The Related Techniques Of Supercapacitors

Supercapacitors have been recognized as unique energy storage devices between conventional electrostatic capacitors and secondary batteries. They integrate the advantages,such as the high power density, the high energy density,the long cyclic life,the high efficiency of charge/discharge and no pollution. When working with batteries, they can meet the high power out-put need of electric vehicles when starting-up or accelerating.They could also be used as electric components and power sources for small apparatus or direct current switches. Supercapacitors have become a research hotspot because of their wide application prospect. According to the principle of energy-storage, there are two types of supercapacitors: electric double-layer capacitors and faraday pseudocapacitors. Electrode materials mainly includes carbon materials, metal oxide and conducting polymer.With high specific surface nano-carbon and cheap oxidated nickel hydroxide as electrode materials for supercapacitors, this dissertation has investigated the preparation and capacitive property of electrode materials and the mechanism of forming capacitance. The token of the electrode materials have been characterized by X-ray diffraction (XRD) and X-ray photon spectra (XPS), while the capacitive characteristics of the electrodes have been investigated by integrating galvanostatic charge/ discharge test. The main results are as follows: 1. High surface area activated carbon for supercapacitors has been prepared fromsoft coal by activation with alkali metals hydroxid through microwave radiation. The advantages of the microwave irradiation including little pollution, high heating efficiency and easy operation. The microwave radiation time and the content of KOH have important effects on the adsorption,the yield and capacitance performance of activated carbon during the activation. The specific capacitance of the activated carbon reaches 72.4F/g and methylene blue adsorption value are 598mg/g when the ratio of KOH to soft coal is 3:1 and the power and radiation time of microwave are 800W and 7 minutes respectively. Using the above activated carbon as electrode materials, the supercapacitor has good charge/discharge properties. It can discharge not only at the small current condition in long time, but also at the large current condition in short time. It also has excellent cycle stability. The capacity of supercapacitors drops no more than 5 percent after 400 cycles.2. Electrochemical performance of carbon-based electric double-layer capacitor at various anode/cathode mass ratio in KOH electrolyte was measured through double-electrode galvanostatic change/ discharge measurements. When the mass ratio of anode/cathode is 1.5 : 1, the specific capacitance of capacitors can reach 62.6F/g which is the maximum, while the working voltage of capacitor could be up to 1.2V and energy density can be effectively improved;Furthermore, the capacitor is of minimal equivalent resistance and prime power performance.3. Oxidated Ni(OH)2 powder was added into activated carbon as positive electrode materials for hybrid capacitor to get a higher working voltage. Through galvanostatic change/ discharge measurements, it was found that the working voltage of the hybrid capacitor could be up to 1.3V. Moreover, the energy-storage density of the hybrid capacitor is 70%-85% higher than that of the C/C capacitor. In addition, the hybrid capacitor has long cycle life and low self-discharge rate.