Research On Spread Rule Of Thermal Runaway Of The Battery Pack

In recent years,the world’s traditional fuel vehicle industry is comprehensively transforming to environment-friendly renewable energy.Lithium-ion batteries are widely used in the core energy storage system of power vehicles because of their large specific energy and multiple cycles.Some automotive energy storage systems are composed of thousands of single batteries in series and parallel,and the thermal runaway accidents of module batteries caused by the abnormality of single or multiple batteries in battery modules occur frequently,which has aroused widespread concern in the society.Therefore,it is of great practical significance to study the thermal runaway of lithium-ion batteries and the spread law of thermal runaway of battery packs.In this paper,the thermal runaway and spread mechanism of lithium-ion battery are analyzed,and three platforms of overcharge,extrusion and puncture are built.Relying on the experimental platform,the influence of abuse mode on the thermal runaway of 21700Lithium-ion Battery is explored.The puncture mode is selected to study the influence law of battery cathode material and model on the thermal runaway of battery.Finally,the thermal runaway propagation law of 21700 Lithium-ion Battery module is studied.The main contents and conclusions of the study are as follows:（1）Taking the fully charged 21700 Battery as the experimental object,the effects of different abuse conditions on the thermal runaway of lithium-ion battery were studied by using three abuse methods:extrusion,puncture and overcharge.It was found that extrusion and overcharge could not trigger the thermal runaway of lithium-ion battery,and the increase of extrusion degree would lead to the leakage of trace electrolyte.The greater the overcharge rate,the highest temperature on the battery surface and the larger the voltage,but it will open circuit and cool down after the voltage rises by 0.87v.Puncture can induce serious thermal runaway reaction of battery cells,and the moment of puncture is accompanied by a large number of active substance injection and violent combustion.Therefore,under the condition of full charge,the consequences of puncture abuse are the most serious.（2）Seven lithium-ion batteries with different models,cathode materials or ratios and charging states were selected to study the thermal runaway after puncture.It was found that the reduction of charging state would reduce the battery surface temperature and the degree of runaway,and the battery with puncture charging state of 0 could not touch the heating runaway.The experimental study of puncture thermal runaway of different cathode materials showed that the stability was stable:LiFePO4<LiCoO2<LiNi_xCo_yMn_zO₂.The higher the nickel content,the more intense the thermal runaway reaction of the battery.The safety valve has a great impact on the surface temperature of the battery.The maximum surface temperature of the battery without the safety valve is generally higher.（3）Through series-parallel connection of 1×3 arrangement in the 21700 lithium-ion battery pack,the main generator battery was punctured to study the thermal runaway propagation law of lithium-ion battery pack.It is found that the generated batteries spread out of control within 3s of the main generator battery out of control.Due to the large trigger short-circuit current and greater instantaneous pressure inside the battery,the parallel battery pack causes a large number of active substances to burn in vitro,the surface temperature is low,and the degree of thermal runaway spread is lower than that of series and unconnected battery packs.Through the distance difference experiment,it is suggested that the distance between lithium-ion batteries should be 3mm or more without cooling measures.