Mechanical Integrity Of Lithium-Ion Battery Module In Electric Vehicles

With the rapid increase in the number of electric vehicles,the safety of power batteries has received more and more attention.Lithium-ion batteries,with their high energy density,high charging efficiency and long cycle life,have become the main energy carriers for electric vehicles.Lithium-ion battery modules are essential for use of battery cells in automobiles.However,the research for the mechanical integrity of battery modules is relatively scarce.This article systematically and comprehensively studies the safety issues of cylindrical battery modules under the conditions of mechanical abuse from a variety of scales such as cell,module,and vehicle.In this paper,the model of the battery cell is established,and we developed the finite element model of the module based on it.Combined with the short-circuit failure criterion of the battery cell,the effect of the structures of the battery module on the structural response and failure strain of the module are studied under a constrained compressive loading condition.The results show that the packing density has the greatest influence.The battery module with a larger packing density generally has a higher structural strength and a lower failure strain,and the packing mode has a non-negligible effect.However,compared to the packing density,the effect of the packing size is very slight.Secondly,to accommodate the modeling of large battery module in crash simulation of full vehicle,this paper regards the battery module as a uniform and continuous macroscopic material,and extracts the representative unit cells of the module and applies periodic boundary conditions on it to obtain the overall mechanical properties of the module.The elasto-plastic material model is used to establish the homogenized model of the battery module.Due to the effect of the packing density on the mechanical properties of the module,the elastic parameters of the homogenized model are modified according to the packing density.The constrained compression experiments of the battery module and the simulations of the detailed module model are used to verify the homogenized model.The results show that the modified homogenized model can accurately predict the mechanical behavior of module under the 12%compression deformation range with different packing sizes and modes.Since the homogenized model of module can be discreted with a larger mesh size,the computational time of the large-scale battery module can be reduced dramatically.Finally,a battery pack model including a battery module,housing case and protection armour is proposed and embedded into the vehicle model.Then the 100%overlapping rigid barrier collision simulation is performed.Through the orthogonal test simulation analysis for the collision speed and battery pack structures,the effects of these on the battery module safety are comprehensively studied.The results show that the higher the collision speed,the more easily the battery module is deformed and failed.After eliminating the influence of collision speed,the number of battery modules and the thickness of the battery case have a great influence on the safety of the battery module.When the mass of the battery is kept constant,the greater the number of modules,the smaller the module size,and the smaller the thickness of the module box,the safer the battery module.The conclusion of this paper can provide guidance for structural optimization design of battery modules and battery packs.