Abstract:

In the lithium-ion battery energy storage systems, the cell experiences increased force fluctuations over prolonged cycles, which can impact cell lifespan and system reliability. Numerical simulation is an effective tool for predicting the stress state of the cell. By developing a constitutive model that accurately reflects the mechanical properties of the cell and applying it to numerical simulations, we can precisely predict the cell's stress state and provide valuable insights for engineering design. Uniaxial compression tests of the battery reveal distinct nonlinear plastic behavior during loading and nonlinear elastic behavior during unloading. This indicates that a single constitutive model is insufficient to accurately characterize the mechanical response of the cell during both loading and unloading processes. This paper employs two types of constitutive models to accurately represent the cell's behavior, the PE (porous elasticity) model for nonlinear elastic behavior and the CFP (crushable foam plasticity) model for nonlinear plasticity and strain hardening. By using these models, the material parameters from the stress-strain curve obtained from testing are inversed. The core of the cell is treated as a laminated composite, and the PE and CFP models, along with their respective material parameters, are alternately applied to develop the numerical model of the cell. A simulation model is established and numerically solved to match the conditions of the uniaxial compression test of the battery. The stress-strain curve data from the numerical simulation results are compared with the actual test results. The findings indicate that the modeling method accurately characterizes the mechanical behavior of the cell during both loading and unloading processes, with a degree of agreement that meets the requirements for engineering simulation applications.

Key words: lithium ion battery, constitutive model, numerical simulation, uniaxial compression, expansion force