Operando Tracking of Ionic and Electronic Percolation in Electrodes for Energy Storage Application Using AC-in Plane Impedance

Abstract

Achieving efficient electronic and ionic electrode percolation is one of the most important parameters to improve batteries and supercapacitors power performance. Various electrical and electrochemical techniques (Cyclic voltammetry, Electrochemical Impedance Spectroscopy, EQCM, SECM, in-situ XRD, etc) can be used to assess the electronic and ionic transport properties in these electrodes. However, there are only few studies and techniques on tracking the change in resistance of an electrode during electrochemical polarization [1, 2, 3], which plays a key-role on its electrochemical performance.In this study, we propose a new method to achieve operando resistance measurement under alternative current (AC), that we’ll call in-plane impedance measurement, under bias potential. In these experiments, the electrodes are deposited onto an insulating substrate so that, differently from conventional electrochemical impedance spectroscopy experiments, here the electrode in-plane conductivity is measured. Moreover, this method allows for distinguishing the ionic part of the in-plane electrode impedance from the electronic part that appears at high and low frequencies, respectively.In this work, in-plane electronic and ionic transport properties of porous carbon (YP50F) and MXene (Ti3C2) electrode are studied while being fully charged or. During polarization, both the ionic and electronic percolation change with the applied potential for both electrode, that could be associated with electrode volume and conductivity change under potential and/or because of some doping caused by ionic specific electrosorption. This operando in-plane impedance measurement method furthers the fundamental understanding of ionic and electronic transport properties and may turn out to be effective tool to improve the electrochemical performances of capacitive, pseudocapacitive, or battery-like electrodes.