A Multi-scale Simulation Strategy For Lithium-ion Battery And Its Application In Crash Safety Of Battery Pack

Traditional cars that use gasoline or diesel engines will cause serious air pollution,and the energy conversion efficiency of petrol engine is very low.New energy technologies have been rapidly developed due to the requirements of environmental protection.For new energy vehicles,the most practical and effective energy source is electricity.Lithium-ion batteries are widely used in electric vehicles due to their high energy density and non-polluting properties.Lithium-ion battery is a complex coupled system of electrochemistry,thermology,mechanics,etc.Its complexity in material,structure,form and function makes the mechanical performance and failure mechanism of lithium-ion battery very complicated.Especially in the complex environment of the vehicle,the battery is susceptible to mechanical loads such as squeezing and impact,which damages the internal structure of the lithium-ion battery,and the destruction of mechanical integrity for the lithium-ion battery may cause a internal short-circuit,excessive temperature and pressure.There are worse phenomena such as fire and explosion.So,it is very urgent to study the mechanical properties of lithium-ion battery.Therefore,this paper proposes a method to establish multi-scale lithium-ion battery mechanical models by studying the material inside the battery.Then these models are used to evaluate the safety of a battery pack in collision.The following research work is carried out:(1)In order to study the mechanical properties of a single battery,the internal structure of the battery is firstly analyzed.Then compression and tension tests on the anode,cathode and separator and the indention tests on the representative structure of the battery in the relevant studies are studied to provide data for the establishment of the finite element model.Four different finite element models in different scale are established using the nonlinear finite element method,named detailed model,electrode homogenizd model,fully homogenized model and incomplete homogenized model.To simulate the failure progress of the representative structure in the indention tests,constitutive models and failure criteria are established for four models.The computational efficiency of the model is greatly improved by the homogenization method.The simulation results of the four models are in good agreement with the experimental results,and all of them show the mechanical response and ultimate failure of the battery structure.These numerical simulation results can help us to understand the mechanism of failure behavior and short circuit caused by mechanical abuse inside the battery.(2)The finite element models above are applied to the impact safety of a battery pack,and the deformation of the battery pack and the failure of the internal batteries under pole side impact are analyzed.By the mixed utilization of different scales of models,the calculation efficiency can be greatly improved on the premise of accurately representing the short circuit inside the battery,which provides a feasible method for the collision safety simulation of large-scale battery packs.(3)To build the finite element model of ground impact,the geometric model of road foreign body and the kinematic form of the ground impact for the car are studied and different scales models are used to analyze the short-circuit behavior of batteries indside the pack.Then the safety of battery pack in ground impact is evaluated.The research work of this paper is of great value for understanding the mechanical response and short-circuit behavior of the batteries inside the pack during the impact.The using of mult-scale models to analyze the internal short-circuit behavior of batteries indside the battery pack have important value in engineering.