Mapping kinetic limitations in porous electrodes using impedance spectroscopy: A route to optimize electrochemical characterization

Porous electrode models of lithium-ion batteries (LIB) are becoming increasingly popular, while the proper determination of the material and electrode properties remains challenging and costly. In this work, we develop a methodology based on the conventional Electrochemical Impedance Spectroscopy (EIS) to extract most of the kinetics model parameters from a limited number of experiments. Building on our recent work [Woillez & Chandesris 2023], where we derived the EIS analytical solution of the linearized P2D-model, our methodology is based on the careful comparison of the various non-dimensional numbers and characteristics frequencies to discriminate the dominant mechanisms, especially in the low-frequency regime. Applied to original EIS measurements conducted in symmetric coin cell configuration on NMC 811 and graphite electrodes with standard loading at several temperatures, we show that electrolyte properties can be extracted from the NMC electrode measurements. While lithium diffusion in NMC is not accessible with the standard electrode loading and chosen frequency range, lithium diffusion in graphite can be measured, with increasing confidence at high temperature. We further provide experimental recommendations on cell design and operating conditions to improve the discrimination of low frequency phenomena.