Li-ion battery swelling force: Multiphysics coupling modeling and in-situ quantification for safety enhancement

Lithium-ion batteries typically exist in modular configurations, where individual cells are subjected to mechanical constraints upon assembled into groups. During charging, volume expansion of lithium-ion batteries induces substantial internal pressure within the battery pack, a phenomenon whose pressure evolution may compromise battery performance and even safety. To effectively manage the mechanical pressure on batteries, precise identification and quantification of the swelling force generated by expansion effects are critical. This study develops a detailed three-dimensional electrochemical-thermal-mechanical coupled model, incorporating the actual layered structure of batteries. The model enable not only the visualization of stress distribution and deformation patterns across battery layers, but also the quantitative characterization of macroscopic swelling force dynamics. Its accuracy and reliability are rigorously validated against experimental data. Based on the model, reveal that the turning point of swelling force coincides with the moment when the lithiation rate at position P3 increases significantly compared with other positions. Moreover, due to the difference in Young's modulus between cathode and anode active materials, the cathode exhibits maximum stress but minimal strain at the end of charging, whereas the anode shows the opposite trend. This work offers guidance for both battery structural optimization and module assembly design, thereby contributing to improved safety of lithium-ion batteries during operation.