Study On Needle Coke Based Activated Carbon As Electrochemical Capacitor Electrode Material

Electrochemical capacitors (EC), which can charge and discharge rapidly and use for a long time, is considered to be a new energy device between the rechargeable battery and a capacitor. It has many extraordinary properties, such as large capacity, small leakage current, good voltage memory, simple charge-discharge processing, long life and so on. The EC's performance highly depends on the electrode materials. Carbon is an excellent electrode materials of EC due to its high conductivity, wide distribution of pore size, small diffuse resistance, high temperature stability properties, controllable pore structure, low cost and good compatibility compared with other materials.This paper firstly discussed the application of needle coke in EC. Needle cokes were carbonized at different temperatures and then activated.The effect of temperature on pore structure and capacitance were studied in detail. It was found that the surface area of AC7, carbonized and activated at 700℃, is 553.2 m2/g. According to the electrochemical tests, AC7 showed high capacitance and good cyclic property in organic electrolyte. When the current density increased from 50 mA/g to 200 mA/g, the specific capacitance decreased from 150.2 F/g to 136.0 F/g, only 9.45% decline, which showed high capacity and good rate properties. The AC impedance test indicated that the resistance of AC7 is the smallest.Direct activation method was also used to produce needle coke based electrodes. The surface areas and mesoporous rate of NAC7, activated by NaOH, are 869.73 m2/g and 32.56 %, respectively. While those of KAC7, activated by KOH, are 1570.39 m2/g and 10.42 %, respectively. These two samples were used to be electrodes of EC in organic electrolyte. The results showed that NAC7 displayed better cyclic performance than KAC7. When the current density increased, the capacitance of NAC7 declined slower than KAC7. In addition, the specific capacitance of NAC7 only decreased 9.1 % at 800mA/g after 5000 cycles.According to the cycle voltammetry (CV), AC impedance and galvanostatic charge/discharge tests, NAC7 showed the best electrochemical performance. Although the capacitance of AC7 is not higher than KAC7, the results of CV and AC impedance of AC7 are better than KAC7.