Research On Thermal Runaway Triggering Method And Thermal Propagation Suppression Mechanism Of Power Battery Systems

The frequent spontaneous combustion and fire incidents of electric vehicles(EV)have seriously impacted consumer confidence and the promotion of EVs,with lithiumion power batteries’ safety issues being the main concern.Thermal propagation(TP)tests for power battery systems,as the highest requirement and ultimate guarantee for EV safety,are at the forefront of addressing these safety issues.Therefore,this project begins with analyzing and understanding TP tests,aiming to solve the problem of updating and upgrading these tests,improve the scientific formulation of TP test regulations and standards,and promote the safe design of EV battery systems.The specific work includes:Firstly,the global TP test regulations and standards were investigated and summarized,with the proposal to focus on thermal runaway(TR)triggering methods as the key issue in TP test research.The mainstream TR triggering methods were tested,and the external heating method with the greatest application potential was chosen.The influence of different test parameters on the characteristics of TR triggering was deeply discussed.The internal thermocouple technology for power batteries was developed,and a high-precision TR simulation model was established.The decisive role of the heating surface power density on TR triggering was discovered.By calculating the heat flow in the heat transfer process,the rule that the shorter the triggering time,the smaller the energy introduced was obtained,and a map for the optimal heater selection was provided.In the study of TP in battery modules triggered by external heating methods,based on the calculation and analysis of heat flux at the main heat transfer interfaces,the phenomenon of accelerated module TP due to preheating was discovered,explaining the phenomena of accelerated and synchronous propagation in the system-level TP process.Next,the high-frequency induction heating technology with high heating power density was applied to the thermal runaway triggering method for power batteries.Induction heating thermal runaway triggering experiments and module TP experiments suitable for different types of batteries were carried out,demonstrating that induction heating has the advantages of fast triggering speed,low energy introduction,good repeatability,and high reproducibility in thermal runaway triggering results.The mechanisms of battery thermal runaway triggered by different methods were compared,and the pros and cons of different triggering methods were evaluated based on five regulatory test requirements,ultimately determining that induction heating has the best overall performance.TP tests for high-energy-density battery systems based on induction heating were conducted,verifying the feasibility and repeatability of this method in system-level TP test.Finally,based on the non-contact,rapid,and efficient heating characteristics of high-frequency induction heating,an in-situ observation device and technology for power battery electrode TP were developed,achieving a closed-loop research on thermal runaway triggering methods across all sizes from single cells,module levels,system levels,and finally returning to the electrode level.Lastly,facing the future development trend of battery systems,a design solution was researched where the battery is directly integrated into the chassis.A bricklaying battery arrangement scheme capable of dispersing the energy flow of thermally runaway batteries was proposed,and simulation analysis was carried out,obtaining results that suppress TP.A TP suppression theory based on insulation and heat dissipation was summarized.Subsequently,a verification experiment with a real bricklaying module configuration was conducted,obtaining experimental results of TP suppression.Under the premise of achieving TP suppression,research on optimization schemes to reduce the volumespecific energy reduction was carried out.Based on the model,the energy flow paths of different batteries during the TP process were studied,and TP energy flow was visualized using multiple means.By analyzing the temperature and reactant concentration at different times before and after the thermal runaway of heat-affected batteries,the selfheating situation of heat-affected batteries at different heat transfer times was revealed,providing a new perspective for understanding the mechanism of TP.This research offers a new approach to solving the pain points and difficulties of TP test,focusing on enhancing the scientific selection of heater parameters in TP test.A novel rapid thermal runaway triggering technology was proposed and systematically verified,providing new solutions for TP test standards and regulations.At the same time,for novel battery system structures,a new configuration capable of suppressing system TP and minimally reducing system-specific energy was proposed,providing technical support for battery system safety design and evaluation.