Evaluating the Determination of Solid-Phase Diffusion and Reaction-Rate Constant For Li-Ion Batteries

Abstract

Physics-based models are important tools for improving Li-ion battery performance, with their accuracy heavily dependent on key parameters such as the solid-phase diffusion coefficient (Ds) and reaction-rate constant (k0). In this work, galvanostatic intermittent titration technique (GITT) and potentiostatic intermittent titration technique (PITT) measurements were conducted on half-cells with a LiNi0.4Co0.6O2 electrode from a commercial battery. Ds and k0 were determined using Weppner and Huggins' 1977 analytical method and physics-based optimization with the DFN model. These parameters were then implemented into the DFN model and validated under constant current with varying current densities and dynamic cycles. The combination of GITT measurements with the DFN model achieved the highest accuracy (average RMSE of 12.6 mV), while the analytical approach showed lower accuracy, especially with GITT (average RMSE of 53.7 mV). Findings indicate that the widely used analytical method with GITT measurements are unsuitable for accurately estimating Ds and k0 due to inherent limitations and assumptions. The proposed DFN model approach with GITT measurements demonstrated high accuracy and versatility in determining Ds and k0 across lithiation levels. Sensitivity analysis further revealed that using the initial relaxation region of the GITT pulse is optimal for estimating Ds with the analytical approach.

Keywords: Batteries, battery modelling, DFN model, galvanostatic intermittent titration technique (GITT), Potentiostatic intermittent titration technique (PITT), Diffusion coefficient