Revisiting EIS-Derived Li+ Diffusion and Charge Transfer Resistance in NMC: Systematic Errors Induced by Neglecting Electrolyte Diffusion and Pathways for Model Correction

<jats:p>Accurate determination of lithium diffusion coefficients in active materials is crucial for the parametrization of physics-based lithium-ion battery models. This work investigates the validity of the EIS-based method proposed by Charbonneau et al. for determining lithium diffusion coefficients in NMC, particularly the assumption that electrolyte diffusion can be neglected. A parametrized DFN model implemented in PyBaMM was used to generate EIS spectra, which were analysed using the corresponding ECM approach. Fifty NMC parameter sets and two cell designs were evaluated to quantify the introduced errors and identify the method’s applicability range. The results show that neglecting electrolyte diffusion can significantly affect the extracted parameters. Four modifications are proposed, substantially improving accuracy with minimal additional complexity. The findings highlight the need to consider electrolyte transport effects in diffusion coefficient determination methods.</jats:p>