Numerical Simulation Of Heat Transfer Performance Of Li-ion Power Battery And Prediction Of Thermal Runaway

In order to alleviate the fossil energy crisis and protect the environment,China is vigorously promoting the development and application of new energy vehicles represented by electric vehicles.Lithium-ion power batteries are the most widely used in electric vehicles.Although lithium-ion power batteries have the advantages of higher energy density and cycle life,lower self-discharge rate,no memory effect,and no pollution,but they also have a serious security issue with thermal runaway.In order to improve the safety performance of lithium-ion power batteries for vehicles,a battery thermal management system is required to control the temperature of the power battery within a range suitable for its operation,while ensuring that the temperature difference in the battery pack is within a certain range.Therefore,this paper studies the influence of ambient temperature on the performance of lithium batteries and the mechanism and prediction of thermal runaway of lithium batteries.This paper takes square and cylindrical lithium iron phosphate batteries as research objects,and quantitatively analyzes the influence of ambient temperature on the temperature rise of single-cell constant current discharge.The influence of ambient temperature on the temperature field of the18650 li-ion battery pack under air cooling is analyzed by simulation.By means of thermal abuse model,the thermal runaway mechanism of lithium battery is further explored by means of heat abuse model and the prediction model of thermal runaway is verified.The main work of this paper can be summarized as:(1)Brief introduction of lithium-ion power battery for vehicles.This paper summarizes the external thermal management methods of lithium batteries,the mechanism of thermal runaway and the experimental methods for inducing thermal runaway;briefly introduces the working principle of lithium batteries;and summarizes the lithium battery heat generation model proposed in the research.(2)Numerical simulation of the effect of ambient temperature on single cells.Decouple the ambient temperature from the relationship between current and state of charge,and a function relationship formula between the ambient temperature and the DC internal resistance of the battery was established.Considering the heat generation model affected by the ambient temperature,the temperature fields of the constant current discharge of the two types of lithium batteries at different discharge rates were transiently simulated and compared.(3)Numerical simulation of the thermal state of the battery pack considering the influence of ambient temperature.The heat generation model considering the influence of the ambient temperature and the heat generation model not considering the influence of the ambient temperature are applied to the battery pack,and the temperature distribution of the battery pack under the two models is compared.The influence of ambient temperature on the temperature distribution of the battery pack under the condition of air cooling is analyzed.(4)Research on the mechanism of thermal runaway of lithium battery and prediction of thermal runaway.The thermal runaway mechanism of the lithium battery is studied in depth through the thermal abuse model;the thermal runaway mechanism and conditions are further explored using thermal abuse numerical simulation;the mathematical model for predicting the thermal runaway of the lithium battery is introduced and verified at the same time.