The Multi-physics Field Modeling Analysis And Structure Design Of Li-ion Battery Module In Deformation Mode

The Li-ion batteries are used as vehicle power battery because of their high energy density,high power density and long cycle life.However,there are still some issues in the application of Li-ion batteries.For example,the batteries will swell or even burn and explode when the batteries are over-deformed due to the external force or the temperature of battery is too high.Therefore,the application and safety of the Li-ion battery have been the important issue that many researchers pay attention.A new structure of battery module which is used to be assembled into vehicle battery pack is designed in this study.Compared with other battery module structures,this structure is based on honeycomb structure and uses grid to reinforce its strength.Moreover,this structure can better protect the internal batteries and improves the safety of the battery pack.In the design process,to obtain the material parameters of Li-ion battery and construct the finite element(FE)model of the battery,the inverse techniques based on the data of flat compression test is used.Meanwhile,a novel space mapping(SM)algorithm is suggested to efficiently optimize the battery module structure due to the expensive computational cost for each evaluation of battery module model.The result shows that the magnitude of stress and the distribution of stress are well improved significantly and the computational cost of optimization for the problem is also decreased significantly compared with the traditional optimization algorithms.A new equivalent circuit model of the deformed Li-ion battery is developed in this study.Moreover,a deformed related parameter is introduced into the new equivalent circuit model,so that the parameters of the circuit elements of the model are related to the state of charge,the temperature of the battery surface and the deformation of battery.Then,the parameters of the circuit elements are identified by a differential evolution algorithm based on the data obtained from these pulse discharging tests of deformed batteries.In addition,the data from the pulse discharging tests of batteries with other deformations and the data from the pulse charging tests of batteries are used to verify the parameters.The results show that the capacity of the batteries drops significantly when the batteries are severely deformed,but the batteries still can charge and discharge.Most importantly,the novel equivalent circuit model can accurately predict the dynamic electrical response of both deformed batteries and intact batteries.This study constructs the multi-physics field coupling model of the deformed battery module based on the battery module FE model,battery thermal model and the equivalent circuit model.The parameters of the constructed equivalent circuit model are related to the deformation displacement and the batteries usually do not undergo uniaxial compression deformation,therefore,in this study,the corresponding relationship between the equivalent plastic strain and the deformation displacement of batteries during compression is established.It makes the parameters of the equivalent circuit model related to the equivalent plastic strain.Moreover,the validation of the transformation of displacement and strain and the applicability of the equivalent circuit model in multi-direction deformation of batteries is verified by the multi-direction deformation tests of batteries.This study constructs the electro-mechanical-thermal coupling model of single battery firstly due to the expensive computational cost of battery module model.The result shows that when the battery is compressed,the temperature variation of the battery which discharg e at constant current is very small.Therefore,the temperature variation of battery module during compression is ignored,and the temperature development of battery module when the battery module continues to discharge after deformation is simulated.The results show that the temperature difference of battery module is significant and the maximum temperature of battery module is high under natural convection conditions.Therefore,the force convection heat dissipation of battery module is carries out in this study.Finally,the temperature difference and the maximum temperature of battery module have been significantly improved after heat dissipation.