Evaluation of electrochemical performance of supercapacitors from equivalent circuits through cyclic voltammetry and galvanostatic charge/discharge

Conventional methods used to analyze electrochemical performance of supercapacitors are complex and cannot illustrate the asymmetrical behavior of charge and discharge curves and the variation of resistance with scan rate and current density. In this work, we propose a simple method to calculate total capacitance and internal resistance of supercapacitors with equivalent circuits and discuss the mechanisms responsible for the asymmetry of galvanostatic charge discharge (GCD) curves. Using the equivalent circuits, we demonstrate the feasibility of analyzing electrochemical performance of supercapacitors from the current-voltage curve for cyclic voltammetry (CV) and the GCD curves for galvanostatic cycling. A series of supercapacitors are constructed, in which the electrodes are pre-compressed under a compressive stress in a range of 1– 7.5 MPa. The experimental results reveal that the total capacitance of the supercapacitors increases with increasing the pre-compressive stress and validated the proposed method. Increasing the pre-compressive stress likely can improve the electrochemical performance of supercapacitors. The results from the analysis with the analytical relations for the resistance of the resistor in parallel connection in the three-element circuit approaching infinity exhibit similar trends to the corresponding ones from the conventional methods in contrast to the results from the three-element circuit, which exhibit different trends. The three-element circuit with the resistor in parallel connection approaching infinity can be used to analyze the electrochemical performance of supercapacitors for both the CV and GCD operational conditions.