Dynamic Effect And Temperature Effect In Lithium-ion Battery Deformation Response Under Indentation

With the continuous increase in the global market share of electric vehicles,the safety of lithium-ion batteries induced by mechanical abuse has attracted more and more attention from enterprises and society.In real electric vehicle crash conditions,impact speed,impact direction and working temperature of the battery may affect the degree of damage.The thesis starts with the multi-condition mechanical indentation tests of the battery to reveal the dynamic effect and temperature effect of the mechanical response of the battery structure.A coupled homogenized model including dynamic and temperature effects as well as Poisson’s ratio effects for battery is developed.It provides a finite element simulation model for safety analysis and design of battery c ell.In this study,static and dynamic indentation tests along different loading directions are firstly performed on the prismatic batteries and jellyrolls.It is found that for the mechanical abuse condition with the main stress state of compression in the out-of-plane direction,the stiffness of jellyrolls and battery cells before failure significantly increases with the increase of loading speed.For the compressive loading condition in the in-plane direction,the dynamic effects of batteries and jellyrolls are weaker than those in the out-of-plane direction.The reason is that the buckling of the structure or the spreading of the multilayer structure of jellyroll easily occurs in the indentation tests along in-plane direction.Then indentation tests on p ouch cells on substrates with different hardness with different loading speeds are carried out for the pouch battery.The results show that the dynamic strengthening effect in different conditions shows different properties.The reason is the influence of different stress states of the battery during the mechanical loading process.Mechanical tests at different temperatures are conducted from three levels of battery cells,jellyrolls and components,and the mechanical properties at different levels related to temperature are summarized.It is found that for the prismatic battery cells,jellyrolls and pouch cells,the structural stiffness of the battery will decrease with the increase of environmental temperature.In addition,the mechanical tests of the comp onent materials at different temperatures are also carried out.The secondary development and extension of the honeycomb material anisotropic model in the existing commercial finite element software is carried out.The anisotropic dynamic effect characteri stics and the temperature effect description function are expanded,and the battery homogenization model is improved for prediction ability of battery mechanical response under different loading speeds and directions.The simulation results show that the e xtended model has a high degree of fit for the mechanical behavior of the jellyroll at different indentation speeds and different temperatures.The homogenized equivalent model of battery cell is further improved.On the basis of the original anisotropic model,a coupled material model with an influence relationship between the components of stress and strain in the principal directions is established.The material model is realized by user-defined subroutines and a representative volume element model is established to calibrate the material parameters.Simulations of several mechanical indentation conditions on jellyroll are conducted and the results show that the coupled material model can predict the mechanical behavior of the jellyroll before the failure moment more accurately compared to the original homogenized model.