Thermal Runaway Initiation And Propagation Of Lithium-ion Traction Battery For Electric Vehicle:Test,Modeling And Prevention

Lithium ion traction battery is the core power source of the current renewable energy vehicles.The safety of lithium ion traction battery arouses wide concerns throughout the world.Thermal runaway is a critical problem for the battery safety issues.To guarantee the safety of the passengers and customers,the industry is calling for effective prevention approaches to control the potential hazard caused by thermal runaway,whereas the government is updating test standards,of which the test procedures require technical support.The purpose of this Ph.D.Dissertation is to serve the dual-requirement of the thermal runaway prevention and standard update from the industry and the government.The Thesis has conducted massive work on the mechanism,modeling and prevention methodologies of the battery thermal runaway.Based on the accident investigations and literature review,the accident can always be divided into three stages: thermal runaway initiation,thermal runaway occurrence,and thermal runaway propagation.The safety management should focus on the stage-by-stage prevention of thermal runaway.On the mechanisms of thermal runaway occurrence,the research solves the problem of adiabatic testing of thermal runaway for large format lithium ion battery.A calibration approach has been established based on the working mode of the extended volume-accelerating rate calorimetry.The good calibration leads to successful adiabatic tests with correct results for the thermal runaway features of large format lithium ion battery.Furthermore,adiabatic test with early termination is proposed to freeze the status of the battery during thermal runaway testing.The electrochemical-thermal coupled mechanisms during thermal runaway testing has been revealed,and a coupled thermal runaway model is built.Furthermore,a model-based algorithm to evaluate the level of battery safety has been proposed to provide early warning of thermal runaway.On the thermal runaway propagation,the research solves the test problem of the temperature distribution within large format lithium ion battery by a method with techniques on the reconstruction of the internal temperature.Experiments have been conducted for penetration induced thermal runaway propagation within large format lithium ion battery module.The thermal runaway propagation mechanism has been revealed.Thermal runaway propagation models,including a lumped model with thermal resistance and a 3D model,have been built.4 possible prevention approaches for thermal runaway propagation have been proposed based on the modeling analysis.On the thermal runaway initiations,the research focuses on the internal short circuit,which is one of the most common characteristics among varies kinds of thermal runaway intiations.A substitute test approach is proposed to simulate the internal short circuit by experiment.A 3D electrochemical-thermal coupled model for the internal short circuit simulation has been built and can be validated by the experimental data.The modeling analysis provides guidance to develop the detection algorithm of the internal short circuit.Moreover,a model-based internal short circuit detection algorithm has been proposed based on the “mean+difference” model,which is a useful approach for the fault diagnosis of system.The internal short circuit detection algorithm can detect internal short circuit fault before the fault develops into thermal runaway.The research provides guidance for the pack design of BMW,and for developing the battery management algorithm of CATL.The techniques of testing and modeling developed in the Dissertation support the establishment of correlated safety standards for electric vehicles.