Energy storage performance of electric double layer capacitors with gradient porosity electrodes

Abstract

• Novel gradient and double-layered porous electrodes are applied. • ELDC performance is related to the location of electrolyte accumulation at large discharge rate. • More advantage occurs in EDLC of the electrode with stepwise and linear increasing porosities. • Porosity variation amplitude serves as an important factor. The variations of porosity in porous electrode influence the performance of electric double layer capacitor (EDLC) greatly. Four kinds of novel porous electrode structure, i.e. linear increasing porosity, linear decreasing porosity, stepwise increasing porosity, stepwise decreasing porosity are applied in the EDLCs. The numerical simulations are conducted to study the effect of porosity distribution in porous electrode on the electrolyte concentration, voltage, specific capacitance and energy in EDLC. In comparison to the electrode with fixed porosity, the higher specific capacitance, higher specific energy and less voltage loss caused by non-uniform electrolyte distribution occur in the EDLC with the porous electrodes in stepwise or linear increasing porosity distributions. The ELDC performance is related to the location of electrolyte accumulation in the electrodes at large discharge current density. The variation amplitude of porosity, whole electrode thickness and initial electrolyte concentration influence the behaviors of EDLC greatly. Thus, the high performance of electric double layer capacitor can be obtained in its porous electrodes with stepwise or linear increasing porosity.