Determination of the Solid State Diffusion Coefficient of Li-ion Battery Single-Phase Materials Using Thin Model Electrodes

For lithium-ion batteries, the development of physico-chemical battery cell models has gained momentum. A significant challenge is the determination of the solid-state diffusion coefficient ( D s ) in the active materials particles, as typically studied porous electrodes are not limited to pure solid-state effects. This work aims to develop an optimized methodology for model parameterization, improving upon the conventional Galvanostatic Intermittent Titration Technique (GITT) on porous electrode systems. Various methods are compared using a single particle model, identifying the GITT-Kang method and Impedance-Fitting as promising advancements. These methods are applied to thin electrodes consisting of a single-layer microstructure of spherical NMC622 particles (model electrodes), demonstrating an almost complete agreement with theoretical principles. For experimental application, the GITT-Kang method is preferred and adapted for the underlying microstructure. Model electrodes with minimal lithium salt concentration in the electrolyte are found to improve the determination of D s and used to investigate the dependency of solid-state diffusion coefficient on lithium stoichiometry and temperature. A comparison with porous electrodes reveals consistent deviations with increasing layer thickness, highlighting the need for methodological advancements for these systems. The presented approach using model electrodes will serve as a reference for future work.