Load Deformation Failure Test And Simulation Analysis For Internal Configuration Of Prismatic Lithium-ion Batteries On New Energy Vehicle

With the rapid growth of the number of electric vehicles(EVs),the corresponding safety problems have become increasingly prominent.In electric vehicle collision accidents,the deformation failure of lithium-ion battery(LIB)under mechanical abuse is one of the factors leading to internal short circuit and thermal runaway.This paper reveals the mechanical behavior and deformation failure of prismatic LIB under mechanical loading through three methods of experimental analysis,simulation and theoretical analysis,establishes the mechanical model to predict the deformation failure of battery structure,improves the cognition of internal short circuit failure of prismatic LIB under mechanical abuse.The mechanical response characteristics and deformation failure modes of prismatic LIB are analyzed from mesoscale and macroscale,which provide valuable reference for test methods,modeling and simulation of prismatic LIB.The mechanical abuse tests of prismatic LIB with different loading directions,loading speeds,SOC States and different types of indenters were carried out,and the effects of these factors on the mechanical characteristics of the battery were analyzed.According to the macroscopic mechanical response curve,open circuit voltage and surface temperature curve,the relationship between mechanical loading and internal short circuit was analyzed.The sudden change point of load was taken as the sign of internal short circuit,and the influence of battery mechanical failure on open circuit voltage and surface temperature was summarized.In addition,uniaxial tensile test,uniaxial compression test and biaxial indentation test were carried out to analyze the mechanical behavior and failure mode of cathode,anode and separator under mechanical abuse.The isotropic compressible foam material of Lsdyna software is used to construct the homogenization model of prismatic LIB.The maximum principal strain failure criterion is used to predict the force-displacement curve and internal short circuit failure under different mechanical loading conditions.The force-displacement constitutive relation of prismatic LIB under spherical indenter was derived by analytical method.The Mohr Coulomb(MC)fracture criterion was introduced to investigate the fracture behavior of the homogenization model of prismatic LIB under local loading,and the failure mode of shear fracture of the interior was analyzed.According to the maximum shear theory,the initial position of interior failure in the homogenization model is predicted and verified by numerical simulation.The dynamic effect of mechanical response of prismatic LIB was studied and analyzed.Based on the homogenization model of prismatic LIB,the side rigid pole impact model of EV is established,and the reliability of the model is verified.The internal fixed structure of the power battery pack,the collision safety of the battery module and the battery cell are analyzed by simulation.Based on the mechanical test of the internal component of prismatic LIB,the mechanical behavior and damage failure of cathode,anode and separator under uniaxial tension,uniaxial compression and local loading were studied.The stress-strain constitutive models of currentl collector,coating material and separator are proposed.The constitutive model of internal components was transformed into mechanical model for analysis and verification,and an axisymmetric mechanical model composed of internal components alternately stacked was constructed.The progressive deformation failure behavior of electrodes between different layers under local loading was simulated and analyzed.There are two different failure modes of PP separator under different sizes of spherical indenter.According to the local loading test of prismatic LIBs,it is found that most batteries have internal short circuit behavior under predictable load and deformation conditions,while a few batteries have larger deformation and do not show internal short circuit behavior.It is found that two different failure modes of PP separator will lead to different internal short circuit behavior of prismatic LIB,and the special failure mode of separator will lead to internal micro short circuit of prismatic LIB.The nonlinear force-displacement constitutive equation was proposed and verified by fitting the force-displacement curve of special failure mode of PP separator under spherical indenter.The mechanism of micro short circuit in prismatic LIB was analyzed by means of experiment combined with theory.The critical deformation criterion of PP separator under special failure mode was proposed.The criterion can be used to evaluate the safety of prismatic LIB under external mechanical force.The research on the mechanism of micro short circuit in LIB caused by separator in special failure mode can help to improve the understanding of EV accident and the protection of LIB in EV.A multi-scale,multi-physical field and multi-interface macro-mesoscopic combined model of prismatic LIB was constructed.Through the simulation analysis,it is found that the computational efficiency of the discrete layered structure model is low due to the multi-layer interface contact.In order to find a balance between the calculation efficiency and the accuracy of the model,an ultra-thin analytical element model was proposed,which consisted of separator,cathode(collector and coating),separator and anode(collector and coating).The deformation failure of the analytical element model was analyzed in detail by spherical indenter,and the results were compared with the experimental results.Furthermore,the analytical element-homogenization multi-scale combined model with high computational efficiency is constructed.The force-displacement curve and failure mode under local loading are simulated by calibrating the number of analytical elements and the failure strain of separtaor.The stress triaxiality and rod angle parameters are introduced to analyze the stress state of the maximum principal strain element in the interior of the combined model.The failure mode of the analytical element model under local loading is analyzed,and the reliability of the model accuracy is verified.The combined model can effectively predict the force-displacement response curve,internal separator deformation failure and internal short circuit displacement of prismatic LIB,and the computational efficiency is greatly improved compared with the discrete layered structure model.Therefore,the combined model can be applied to pack or EV,which can ensure the simulation accuracy and control the development time reasonably.