Self-Discharge Characterization and Modeling of Electrochemical Capacitor Used for Power Electronics Applications
The self-discharge of an electrochemical capacitor, also referred to as a supercapacitor, is an important factor in determining the duration of maintaining stored energy, especially in low-duty-cycle applications. The study of self-discharge is conducted as follows: first, the self-discharge is characterized by measuring the decline of open-circuit voltage of the electrochemical capacitor. Second, the mechanisms of self-discharge, leakage current, and diffusion of ions at the electrode–electrolyte interfaces are modeled by an electrical equivalent circuit. The equivalent circuit elements are experimentally determined according to the self-discharge time behavior. In addition, the dependence of the self-discharge parameters on both temperature and initial voltage across the electrochemical capacitor is described in detail.
OVER years, electrochemical capacitors have acquired many names coined by manufacturers including supercapacitors, ultracapacitors, double-layer capacitors, etc. Electrochemical capacitors are used more and more for storing electrical energy in different fields, for example, in communications, electric and hybrid vehicles, etc. They offer interesting electrical characteristics and high-lifetime cycling compared to that of batteries . An electrochemical capacitor stores energy by two processes. The main process is by the separation of positive and negative charges at the interfaces between the electrode and the electrolyte. This phenomenon is called double-layer capacitance. The second technique stores charge by reversible Faradic redox processes (electron-transfer reactions between the electrodes and the electrolyte) . These components can lose their stored energy fast compared to chemical cells, particularly at high temperatures and voltages
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