Electrochemical Capacitor Electrode Material And Its Electrical Storage Performance

Electrochemical capacitors (ECs), as one of new energy storage devices, are characterized with high power density and long life time, etc. ECs have potential applications in the fields of mobile communication and electric vehicle, etc. Recently, study on ECs is mainly focused on the preparation and structure adjustment of high performance porous electrode materials.In this paper, activated carbons (ACs) were prepared by microwave heating petroleum coke or coal with KOH as activation agent. ACs were investigated by Fourier transform infrared (FT-IR) and N₂ adsorption technique. ACs were subjected to heat or hydrochloric acid treatment to improve AC performance. Hydrous RuO_x/activated carbon black (ACB) composites were successfully prepared by a chemical impregnation method for ECs. ECs were assembled using AC-based electrode materials as the base materials. The electrochemical performance of ECs was evaluated by cyclic voltammograms (CVs), charge-discharge at constant current and electrochemical impedance spectrum (EIS). The main results are as following.1. The specific surface area and total pore volume of ACs from petroleum coke goes through a maximum with the increase of activation time or KOH/coke ratio. The specific capacitance of AC electrodes and energy density of AC capacitors show the same change trend as the specific surface area and total pore volume. ACs with the optimal performance are obtained at the microwave power of 250 W for 35 min activation time at KOH/coke ratio of 5:1 (AC is referred as AC5/1). The specific surface area and total pore volume of AC5/1 reaches 2312 m² g^-1 and 1.13 m³ g^-1, respectively. The corresponding electrode has better electrochemical performance. The specific capacitance of AC5/1 at 50 mA g^-1 current density decreases from 342.8 to 246.0 F g^-1 after 1000 charge?discharge cycles with 71.8% capacitance retention. The energy density of AC5/1 capacitor remains at 7.9 Wh kg^-1 after 1000 cycles and its energy density retention is 68.5%. The capacitance retention ratio of AC5/1 heated at 1073 K reaches 75.1%. The peak intensity of ?C=O at 1633 cm?1 on AC5/1 becomes weak after 1000 cycles.2. ACs are prepared from five different coals under the above optimal activation condition. ACs as-prepared are microporous carbons containing a few mesopores, of which the content of mesopore volume amounts to 50.0%. The total pore volume of ACs from different coal goes through a maximum with the decrease of volatile mater content in coals. The specific surface area and total pore volume of coal-based ACs are in the range of 748-1874 m² g^-1 and 0.45-1.0 m³ g^-1. The specific capacitance of coal-based ACs ranges from 165.3 to 269.3 F g^-1 at 50 mA g-1 current density. The energy density of coal-based AC capacitors reaches 8.6 Wh kg^-1 when its power density ranges from 0.02 to 0.25 kW kg^-1. The specific surface area and total pore volume of ACs from coal is lower than that from petroleum coke, respectively. 3. Amorphous hydrous RuO_x structure retains in the composite heated at 423 K. The internal resistence of the composites almost increases with the increase of RuO_x content in the composites. The specific capacitance of the composites increases with the increase of RuO_x content in the composites while the specific capacitance of RuO_x decreases from 1255.8 to 533.7 F g^-1. The utilization of RuO_x decreases with higher loading RuO_x on ACB.