Study On Thermal Runaway And Propagation Law Of Lithium-ion Power Battery

With the wide application of lithium-ion batteries in new energy electric vehicles,electrochemical energy storage,mobile electronic devices and other fields,fire and explosion accidents caused by thermal runaway of lithium-ion batteries occur from time to time,causing serious casualties and property losses.In this paper,the triggering mechanism of thermal runaway and the heat transfer mechanism of thermal runaway propagation of lithium-ion batteries are studied by combining experimental and numerical simulation methods,which is of great significance for the promotion and application of lithium-ion power batteries in the field of new energy.In this paper,the heat abuse experiment of 5Ah NCM soft pack lithium-ion battery unit and battery module was carried out.The temperature rise of combustion and flue gas in battery and gas producing area,the change of heat flux and gas content of convection and radiation heat transfer,the heat flux of heat conduction between battery packs,and the quality change of single battery and module were analyzed.The results show that radiation heat transfer plays a dominant role in the thermal runaway spread of lithium-ion battery.When the battery is on fire,the thermal runaway spread rate of the battery pack is faster.The more time it takes for the thermal runaway spread to the whole battery pack,the greater the mass loss of the battery pack.The flame temperature of battery jet fire is about 800℃,and the flue gas temperature is about 150℃～350℃.The contents of CO2,CO,H2 and alkanes in the flue gas increase during the thermal runaway and combustion process of the battery.Furthermore,using COMSOL Multiphysics simulation software,the thermal abuse and internal short-circuit induced heat runaway model of single NCM soft pack battery was constructed.Based on the finite rate combustion method,a combustion dynamic model of the battery was established,and the thermal decomposition and temperature rise of the internal materials of the single battery were analyzed;The influence of different internal short circuit positions on thermal runaway of single cell.It is found that the heat required for thermal runaway of the battery mainly comes from the decomposition reaction between positive and negative electrodes and electrolyte.The closer the internal short-circuit position is to the corner,the thermal runaway of the battery is more likely to occur,and the higher the peak temperature of the internal short-circuit position is.Finally,the influence of different number of batteries,different heat source location on the thermal runaway spread of the battery pack is analyzed,and the effectiveness of ventilation control of thermal runaway of the battery pack with different arrangement is analyzed.It is found that with the increase of the number of batteries,the start time of thermal runaway is delayed,but the spreading rate of thermal runaway is greatly accelerated.The thermal runaway time of lithium-ion batteries triggered by the heat source located in the center of the battery pack lags behind that of the heat source located on the side of the battery pack,but the thermal runaway spreading rate is faster.Under the same arrangement,with the increase of wind speed,the thermal runaway of the battery pack is restrained;Under the same wind speed,the triggering time of thermal runaway of vertically arranged batteries is earlier than that of horizontally arranged batteries.