A hierarchical electrochemical-thermal-mechanical coupled model capable of predicting non-uniform behaviors in large-format Li-ion cells

This work presents a hierarchical electrochemical-thermal-mechanical coupled model of Li-ion cells that integrates multiple submodels across particle, electrode, and cell levels. The model divides a single cell into various parallel-connected unit cells, each associated with a physics-based pseudo-2D (P2D) model capable of predicting mass and charge transfers at the electrode level and diffusion-induced stress/strain at the particle level. At the cell level, a heat-transfer submodel calculates the temperature distribution across the cell thickness, along with an electrical submodel to predict current partition and a phenomenological mechanical submodel to estimate force and displacement under preloading conditions. These through-plane submodels are bi-directionally coupled with the P2D models, enabling the translation of particle-level stress/strain changes to cell-level force and displacement evolutions under various preloading conditions. The model is validated against experimental data from three types of cells with different thicknesses, demonstrating its capability in predicting current/voltage, temperature, and displacement/force evolutions at various C-rates and preloading forces. The calibrated model is then extrapolated to explore the coupled electrochemical, thermal, and mechanical behaviors in large-format cells with considerably greater thickness. Significant non-uniformities are observed at two levels: across the electrode thickness and across the cell thickness. The former is associated with non-uniform current densities within a single electrode, leading to varying rates of lithiation/delithiation at different positions and, consequently, varying rates of particle volume changes. The latter is associated with non-uniform current and temperature distributions, resulting in non-uniform reaction-induced and thermal-induced displacement and force.