Capacitance Performance And Model Analysis Of Carbon-based Electrode Materials For Electrochemical Capacitors

Electrochemical capacitors (EC) are energy storage devices with properties intermediate between batteries and traditional capacitors. The commercial success of EC is due to the high power density, high cycle life, extremely low cost. They are mainly used as power backup for electric automobile, wind power generation and industry. Activated carbon with high surface area is usually used as the electrode material since the usable charge stored in EC mainly depends on the surface area with a non-linear relationship. In addition, the pore structure of activated carbon is one of the important factors for capacitance of EDLC.Based on the high surface area activated carbon as electrode material for EC, the relevant research for its testing and modeling is accomplished in deep.(1) The capacitive properties of different electrodes are tested and analyzed by Cyclic Voltammetry (CV), Constant Current Charge-Discharge and Electrochemical Impedance Spectroscopy (EIS).(2) The curve-fitting to impedance spectrum of EDLC is carried out by the assumptions of cylindrical pore with De Levie's theoretical formula in transmission line model (TLM). The contributions of depth and diameter of pore to impedance spectrum were discussed. The test results show that the transition frequency shifts to low frequency side with the decrease of the diameter and the increase of the depth.(3) We propose a triple pore structure model of EDLC with branch pore structure for the first time. Computer simulation of electrochemical impedance with the present electrode model was carried out to characterize the impedance spectrum of EDLC. The simulation results show that the new model is highly fit in with the actual structure.