A Large Deformation and Fracture Model of Lithium-Ion Battery Cells Treated as a Homogenized Medium

Lithium-ion batteries cause serious safety concerns subjected to extreme mechanical loads. Large deformation and fracture can trigger an internal short circuit that may end up with thermal runaway. The high dimensionality of battery systems arising from the multiple length scales (interfaces, electrodes, cells, modules, and packs) and the complex loading conditions (direction, velocity, geometry, state-of-charge, etc.) poses an ever-present challenge to the modeling of mechanical deformation and fracture behavior of batteries. We propose here a practical and accurate computational model based on two assumptions. First, the cell is treated as a homogenized medium mechanically equivalent to its discrete layered structure of alternating electrodes and separators. Second, we fully decouple the mechanical deformation and fracture behavior from the electrochemical processes because, before the fracture and the onset of short circuit, trivial thermal processes are present. Accordingly, an anisotropic plasticity model is proposed to characterize the large deformation of the cell under external loads. The model is enriched by including the state-of-charge and rate-dependence of the plasticity and crack initiation. The model is fully calibrated and validated using a set of experimental data on large-format pouch batteries. The capability of modeling the anisotropy, state-of-charge and rate dependences is shown through numerical simulations.