Modelling of an electrochemical double layer capacitor using cyclic voltammetry

An Electrochemical Double Layer Capacitor (EDLC) bridges the gap between a battery and an electrostatic capacitor in terms of energy and power density. High surface area of the electrode materials and an extremely small thickness of the double layer results in exceptionally high capacitance values compared to electrostatic capacitors. Electrical modeling of the EDLC is crucial for understanding the behavior of the device, and for evolving a better design. Cyclic Voltammetry (CV) is an experimental technique to obtain the overall capacitance of an EDLC. The present work proposes an analytical approach for estimation of the porosity in the EDLC electrode from the CV experiments, with the help of electrical model. A voltage-dependent capacitance model is used to model the charging and discharging behavior of the EDLC. The manner, in which the modeled circuit parameters relate to the shape of the cyclic voltammetry curve, and the physical implications thereof are discussed.

I. Introduction

In any energy storage device, there is a compromise between the energy density (Wh/kg) and power density (W/kg). The Electrochemical Double Layer Capacitor (EDLC), or the Supercapacitor (SC), is a promising candidate in this regard as it has high energy density (comparable to batteries) as well as high power densities (close to that of electrostatic capacitors) [1].