Test And Characterization Of Strain-rate Dependent Mechanical Properties For Component Materials Of Lithium-ion Battery

The rapidly increasing market of new energy vehicle raises the requirements for crash safety development.However,there's no heterogeneous finite element model of battery that can be applied for full vehicle safety development.This study characterizes the ratedependent mechanical behavior of the main component materials of battery,supporting the establishment of heterogeneous model.Firstly,the mechanical behavior of electrodes,current collectors,separators and plastic-aluminum films was characterized through uniaxial quasi-static and dynamic tension tests.The active particle enhanced the load response of electrodes not significantly.The mechanical behavior of electrodes and current collectors was considered to be somewhat rate-dependent.The mechanical behavior of separators was significantly anisotropic and rate-dependent and different fracture modes were found under different loading directions.The microscopic image of separator showed obvious orientation of the prime fibers,which was thought to be highly related to the anisotropy and fracture modes of separator.The plastic-aluminum films were found to be highly rate-dependent and somewhat anisotropic.Furthermore,this study conducted the error sources analysis for the tension tests results,which indicated a good control of uncertainty level whereas for the dynamic tension tests with low load level,the accuracy and robustness of customized load cell should be improved.Subsequently,the uniaxial mechanical behavior of separator was characterized with Parallel Rheological Framework(PRF)constitutive model,which was featured a coupled behavior of non-linear viscoelasticity and plasticity.To calibrate the PRF models,continuous relaxation test was designed to obtain the equilibrium response and continuous loading-unloading test was designed to decouple the elastic and plastic behavior of equilibrium response.The original values and optimization range of the parameters of creep model were obtained through the relaxation procedure under different stress level.Then the parameter optimization was conducted with the objective of minimization of absolute error and relative error.The optimization range of parameters of creep model was extended to improve the modeling result of tension tests under different strain rates according to the result of first time optimization.The influence of extended optimization range,the amount of viscoelastic branch of PRF model and the input method of elastic behavior(defined as instantaneous or long term)was also discussed.Extended optimization range improved the simulation results of tension tests whereas reduced the accuracy of relaxation simulation.More viscoelastic branches didn't guarantee better optimization results.Elastic behavior defined as instantaneous improved the simulation results under dynamic tension and reduced the accuracy of quasi-static situation.Lastly,punch tests and corresponding finite element simulations were conducted for electrodes and separators.The model using elasto-plastic constitutive model and membrane elements accurately predicted the load-displacement response of electrodes under quasi-static punch tests.However,more accurate test data was needed to verify the dynamic simulation results.For the separators which were significantly anisotropic,a finite element model combined of anisotropic linear viscoelastic model and parallel rheological model was promoted,which accurately predicted the load-displacement response under quasi-static and dynamic punch tests.