Evaluation of Electrochemical Techniques for Characterizing the Kinetics of Porous Insertion-Type Electrodes

Abstract

The composite-type porous electrode remains the most commonly used electrode for a wide variety of electrochemical energy storage devices, including lithium-ion batteries, electrochemical capacitors, Li-S/Li-air batteries, and even all-solid-state batteries. This is due to its ease of manufacturability and ability to maintain a high electrochemical surface area with adequate ion and electron transport. Understanding porous electrode kinetics is essential to maximize the active material utilization at high rates. A variety of electrochemical techniques exist to characterize the kinetic behavior of porous electrodes. The most popular ones include electrochemical impedance spectroscopy, galvanostatic charge/discharge, galvanostatic intermittent titration technique, and cyclic voltammetry. The purpose of this work was to evaluate which of these four techniques provides the most relevant kinetic information for understanding porous electrode kinetics. To do this, we utilized porous electrodes composed of LiCoO2 as a model insertion-type material, and with varying thicknesses (10 - 40 µm). We find that GITT is an accessible and reliable method for obtaining the effective diffusion coefficient of the porous electrode. It yields consistent results, regardless of electrode thickness and component ratio. On the other hand, the cyclic voltammetry peak current behavior can be easily compromised, even at slow scan rates of 0.01 - 0.1 mV/s, and when using a high conducting domain ratio. When comparing the dQ/dV plot and cyclic voltammetry for observing peaks indicating phase transitions in the insertion material, the dQ/dV plot is less kinetically limited. We utilized the differential relaxation time (DRT) method to analyze electrochemical impedance spectroscopy data. Our findings demonstrate that as thickness increases, charge transfer resistance decreases, while diffusion resistance increases. This study provides a comprehensive evaluation on the differences between electrochemical methods to characterize the kinetics of composite porous electrodes.