A Study On The Modeling And Simulation Of Thermal Runaway Propagation Of Large-format Lithium-ion Batteries

The safety of traction battery system is one of the important problems that restrict the commercialization of electric vehicles.For the contemporary lithium-ion batteries,thermal runaway is the core scientific problem of battery safety problems,and thermal runaway propagation causes severe haem in practice.Preventing the propagation of thermal runaway in battery modules is an important strategy to ensure the safety of passengers’ lives and property.It is of great significance to develop efficient design tools for the prevention and control against thermal runaway propagation.This thesis establishes an accurate and reliable thermal runaway propagation model of batteries for the thermal safety design of battery pack.Thermal runaway heat generation and gas generation of batteries were evaluated in order to define the descipline of heat generation during thermal runaway in the model,Parameter identification methods for estimating the parameters before and after thermal runaway were studied in order to accurately simulate the heat transfer process in the process of thermal runaway propagation of batteries.The thermal runaway propagation model of battery module was established based on the law of heat generation and heat transfer of batteries.The performance of thermal runaway propagation of battery module was evaluated using the model.The proposed model will benefit the thermal safety management system of battery pack with reduced wost and time.Firstly,the accelerating rate calorimeter(ARC)is used to test the thermal runaway of batteries with different geometries of the same material system.The key thermal parameters and the law of gas generation and heat generation during the thermal runaway of batteries were obtained.The necessity of temperature measurement in batteries is explained through experiments,and the characteristics temperature of thermal runaway for batteries with different packages is analyzed.The thermo-physical parameters of the cell chemistries before and after thermal runaway are measured and identified using the method of local heating and simulation optimization.The method of weight coefficient selection based on sensitivity analysis is introduced in the optimization method.The thermal parameters such as thermal conductivity and specific heat capacity of battery materials can be automatically optimized and identified in the model based on the experimental results.Then,the energy release law of thermal runaway is defined based on the temperature features of the battery.The thermal runaway propagation model of the cell monomer and module is established after introducing the changes of thermal physical parameters before and after thermal runaway of the cell material.The above models are validated by experiment of penetration induced thermal runaway of cell and heating induced thermal runaway propagation of cell module.The results show that the model has high accuracy.Modeling analysis reveals the influence of thermal parameters on thermal runaway propagation characteristics of batteries and its causes.Finally,the inhibition effect of liquid cooling on thermal runaway behaviors of batteries is simulated and verified by experiments based on the thermal runaway propagation model established above.The influence of thermal insulation and heat dissipation conditions on thermal runaway propagation characteristics of battery module are explained by heat flow analysis of the model.The thermal runaway propagation suppression effect of the optimized battery module is verified by model and experiment after optimizing the design of battery module with liquid cooling.