Research On Mechanical Properties Of Lithium-ion Battery Component Materials

As the power source of electric vehicle,the thermal stability,electrical safety and mechanical properties of lithium-ion battery is directly related to the safety performance of electric vehicle.The thermal escape of single battery will spread rapidly in the battery module,which may eventually lead to the thermal runaway of the whole vehicle.Especially in the case of vehicle collision,the dynamic impact condition is more likely to lead to the structural failure of the battery.And the failure of the battery component material is the cause of the structural failure of the battery.The mechanical response of the battery is also closely related to the ambient temperature,state of charge(SOC)and state of health(SOH),so it reveals the real service conditions of the lithium-ion battery at high strain rate and different temperatures,the mechanical response and failure behavior of the components are of great significance to the thermal runaway protection of electric vehicles and the safety design of lithium batteries.Therefore,the mechanical response and failure behavior of prismatic LiFePO4 battery were studied by experiments,numerical analysis and finite element method.The constitutive model of the material was constructed and verified.The specific research contents are as follows:For the purpose of discussing the effect of high strain rate on the mechanical response of battery materials,anisotropic behavior of battery materials were researched,and analyze the basic mechanical behavior of the materials and the performance differences in three different directions.This difference is mainly caused by the production process and packaging process of the material.Then,the strain rate effect of cathode materials with strong brittleness were studied,and found that the effect of strain rate on the mechanical response of cathode materials is not obvious.Finally,the high-speed tensile tests of anode and separator materials in the anisotropic direction were carried out,and the mechanical response of the material under dynamic load and the effect of the change of strain rate on the mechanical response of the material are analyzed.After the test,the samples were scanned by electron microscope,and it was found that there were obvious differences in the surface failure forms with the change of strain rate.The temperature effect of component materials,uniaxial tensile tests on three kinds of materials in anisotropic direction under different temperature conditions were carried out.Through the experimental data,the effected of the mechanical response of materials by temperature were summarized,and analyzed the differences of different materials affected by temperature.It was found that the mechanical response of separator materials was more affected by temperature than that of anode and cathode materials.Then,the samples were scanned by electron microscope,and it was found that the surface failure modes varied with temperature.A constitutive model to describe the mechanical characteristics of materials were established,and to take into account the strain rate effect(except cathode)and temperature effect of materials,describe the mechanical behavior of anode and cathode under full strain by improved Rambery-Osgood model,and describe the mechanical behavior of separator under full strain by improved viscoplastic model Anisotropy in the same direction.Meanwhile,in order to verify the accuracy of the constitutive model,so as to predict the mechanical response of battery component materials and the application of finite element analysis,calculated and analyzed the constitutive model through the finite element software LS-DYNA,and compared with the experimental results,and found that the constitutive model has good accuracy.