Electrochemical Transport Phenomena in Hybrid Pseudocapacitors under Galvanostatic Cycling

Anna L D'Entremont,Hainan Wang,Laurent Pilon,Henri-Louis Girard

doi:10.1149/2.0441602jes

Abstract

This study aims to provide insights into the electrochemical transport and interfacial phenomena in hybrid pseudocapacitors under galvanostatic cycling. Pseudocapacitors are promising electrical energy storage devices for applications requiring large power density. They also involve complex, coupled, and multiscale physical phenomena that are difficult to probe experimentally. The present study performed detailed numerical simulations for a hybrid pseudocapacitor with planar electrodes and binary, asymmetric electrolyte under various cycling conditions, based on a first-principles continuum model accounting simultaneously for charge storage by electric double layer (EDL) formation and by faradaic reactions with intercalation. Two asymptotic regimes were identified corresponding to (i) dominant faradaic charge storage at low current and low frequency or (ii) dominant EDL charge storage at high current and high frequency. Analytical expressions for the intercalated ion concentration and surface overpotential were derived for both asymptotic regimes. Features of typical experimentally measured cell potential were physically interpreted. These insights could guide the optimization of hybrid pseudocapacitors.

Highlights

Capacitance.— The capacitance of an electrochemical capacitor characterizes the amount of electric charge qs stored from the external circuit as a function of the cell potential ψs
The study established that cyclic voltammetry (CV) curves featured a faradaic regime dominated by redox reactions and a capacitive regime dominated by electric double layer (EDL) formation
The present study investigated the electrochemical transport phenomena occurring inside hybrid pseudocapacitors under galvanostatic cycling using a rigorous physical model accounting for coupled EDL formation and faradaic reactions

Summary

Introduction

Capacitance.— The capacitance of an electrochemical capacitor characterizes the amount of electric charge qs (in C) stored from the external circuit as a function of the cell potential ψs (in V). The areal capacitance Cs is defined as the capacitance per unit electrode/electrolyte interfacial area, expressed in F m−2. Cs,di f f and the integral Cs,int areal capacitances can be determined by galvanostatic cycling at constant current density ± js = dqs/dt according to Refs. Cs,i nt qs ψs js tc/2 ψmax − ψmin [1]. Where ψmax and ψmin are the upper and lower limits of ψs (t), and tc is the cycle period (in s). Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract)

Objectives

Results

Conclusion