Multiscale modeling approach to determine effective lithium-ion transport properties

This paper elaborates upon the limitations of using volume-averaged macroscale electrochemical models for lithium-ion batteries, such as the Pseudo-two-Dimensional (P2D) model [1]. To address some of these limitations, an enhanced electrochemical modeling framework that is developed using the homogenization technique is presented in this work. The mass and charge transport equations of the new modeling framework are derived by multiple-scale asymptotic expansion of the pore-scale Poisson-Nernst-Planck (PNP) equations [2]. The effective diffusion and conductivity coefficients of the homogenized model are determined by formulating and solving a closure variable in the electrode microstructure. This paper demonstrates the methodology to calculate the effective transport parameters using the closure approach. We compare the closure-based effective parameters with the effective parameters obtained by using the Bruggeman theory. The Bruggeman approach relies on a simplified approximation of the pore-scale parameters to determine effective values using only porosity. Results indicate that the Bruggeman approach underpredicts the effective transport parameters. This could critically influence model predictive ability, particularly for high C-rates and temperatures of battery operation.