Abstract: Due to the strong nonlinear and multi-scale bidirectional coupling between mechanical deformation and electrochemical processes, involving complex interaction mechanisms from atomic scale to macroscopic scale, it is difficult to accurately analyze the force electrochemical coupling constitutive relationship in lithium battery extrusion deformation. Therefore, this study delves into the extrusion deformation behavior and performance degradation mechanism of lithium-ion batteries. The finite element model is constructed by combining the meso core layer element with the homogenized layer set model. The electrode sheet is characterized by the compressible foam material, and the diaphragm is simulated by the piecewise elastoplastic material. The elastic modulus of the homogeneous layer is calculated by the Voigt average method, and the stress distribution under the 12,24,36 kN extrusion load is simulated by the axisymmetric simplified method. Establishing a force electrochemical coupling model, introducing Larché-Cahn chemical potential theory to quantitatively characterize the influence of extrusion stress on lithium ion migration rate and chemical potential, revealing the electrochemical degradation mechanism of lithium ion redistribution caused by mechanical deformation, breaking through the limitations of traditional single physical field analysis, and providing new theoretical basis for the safe design of power batteries. Research has found that the stress concentration areas inside the battery during the squeezing process are mainly located at the junction of the battery electrodes and separators, and the strain in these areas significantly increases with the degree of squeezing. In terms of performance degradation, extrusion deformation can lead to structural damage to electrode materials, such as detachment of active materials, separation of electrodes and current collectors, and other phenomena. At the same time, it can also affect the diffusion channels of lithium ions, increasing the internal resistance of the battery and accelerating capacity degradation. The results of this study contribute to a deeper understanding of the behavioral characteristics of lithium-ion batteries under compression conditions, providing a theoretical basis for improving the safety and reliability of lithium-ion batteries.

Key words: lithium-ion batteries, extrusion deformation, performance degradation, active substance, internal resistance of battery, finite element analysis