Method for Measuring Solid-State Diffusivity: Part 1. Theoretical Introduction

The reliable determination of solid-state lithium diffusivity is essential for parameterizing physics-based lithium-ion battery models. However, conventional methods misattribute electrolyte concentration polarization to solid-state diffusion, introducing systematic errors in the inferred diffusivity. This study introduces a resistance-decomposition method that explicitly accounts for electronic conduction, electrolyte transport, charge transfer, and solid-state diffusion within the Doyle–Fuller–Newman (DFN) framework. The diffusion coefficient is calculated from the residual polarization resistance after independently determining the other contributions and accounting for the equilibrium potential dependence on the state of lithiation. The method is evaluated using synthetic voltage data generated with the DFN model implemented in PyBaMM. The results demonstrate accurate recovery of the prescribed diffusivity across most of the investigated parameter space under idealized conditions.. These findings establish the theoretical basis and numerical feasibility of the proposed method while identifying key limitations that require experimental validation.