Mechanism And Experimental Research On Thermal Runaway Propagation Inhibition Of Cylindrical Lithium-ion Batteries

As an energy-containing substance,lithium-ion batteries will suffer from thermal runaway under abuse conditions,leading to a danger of high temperature,combustion and even explosion,and when ventilation conditions are limited,the high temperature and flame of the battery can easily transfer heat to the surrounding batteries,triggering thermal runaway propagation,resulting in a larger area of combustion,which seriously threatens the safety of people’s lives and property.Therefore,it is of great significance and value to research thermal runaway propagation inhibition of Li-ion batteries.In this thesis,a combination of theoretical analysis and experimental research is used to focus on the thermal runaway propagation of cylindrical lithium-ion batteries in one-dimensional arrangement,the inhibition mechanism and inhibition process of fluorine-containing gas fire-extinguishing agent on thermal runaway propagation and the cooling effect of the fire-extinguishing agent on lithium-ion batteries were studied.The change characteristics of temperature,combustion behavior,thermal runaway propagation time,mass loss,gas composition and concentration during the thermal runaway propagation process of lithium-ion batteries with different states of charge（SOC）and capacities were analyzed.It is clear that high temperature and flame are the main causes of thermal runaway propagation of batteries,and the calculation model of peak temperature of runaway batteries is established.The results show that thermal runaway propagation of cylindrical lithium-ion batteries with a one-dimensional arrangement is bound to occur.The high SOC batteries has a higher combustion risk and a faster thermal runaway propagation rate,which is mainly manifested in the higher peak temperature,shorter propagation time,greater mass loss,and more intense flame burning of the thermal runaway battery;The low SOC batteries has a higher gas risk,which is mainly manifested in no flame,longer gas release duration and greater output of irritant gas.The main components are NH₃,HCl and HF,accounting for more than50%of the output.Large-capacity batteries have a higher probability of thermal runaway occurrence and propagation,lower thermal runaway trigger temperature,earlier trigger time,and shorter thermal runaway propagation time;small-capacity batteries continue to release gas for a longer time and have higher toxic and harmful and flammable gas accumulation hazards.The peak temperature of the battery is an important indicator for judging whether the thermal runaway propagation of the battery can occur.Based on the experimental data and theoretical analysis,a calculation model of the peak temperature of the thermal runaway of each battery in a one-dimensional arrangement is proposed,which is of great significance for analyzing the variation trend of the highest temperature of the battery and the thermal runaway propagation.Theoretically explores the suppression mechanism of fluorine-containing gas fire extinguishing agent on lithium-ion battery flame.By analyzing the combustible gas components in the thermal runaway of lithium-ion batteries,it is determined that hydrocarbon gases are the main combustibles produced by the batteries.The 2-bromo-3,3,3-trifluoropropene（C₃H₂F₃Br,BTP）fire extinguishing agent and the main combustible methane（CH₄）were selected to analyze the inhibition mechanism of fluorine-containing gas fire extinguishing agent on the flame of lithium-ion battery.The interaction process of CH₄and BTP molecules was analyzed by combining the methods of Ab-initio Molecular Dynamics（AIMD）and quantum chemistry.The results show that the high fire extinguishing efficiency of BTP is due to the fact that the HBr generated by the thermal decomposition of BTP molecules can directly react with H and OH radicals in the flame to inhibit combustion and generate Br radicals,which can also interact with H,OH radicals in the flame to further inhibits combustion.The inhibitory effect of BTP on the flame lies in three aspects:one is the direct interaction between the BTP molecule and the CH₄molecule,which consumes the fuel;the second is the interaction between the BTP molecule and the flame,which interrupts the chain reaction of combustion;the third is that the interaction process of BTP and flame will consume more H radicals than CH4 combustion process,which inhibits the combustion of CH₄.Experimental study on the inhibitory effect of fluorine-containing gas fire extinguishing agent on thermal runaway propagation of lithium-ion batteries.A variety of fluorine-containing gas fire extinguishing agents was used to carry out inhibition experiments on the thermal runaway propagation of lithium-ion batteries.The temperature changes,combustion behavior changes and gas concentration changes of the batteries were compared and analyzed.The experimental results show that releasing a fire extinguishing agent can effectively inhibit the propagation of thermal runaway of lithium-ion batteries,but the danger of irritating gas increases.The inhibitory effect of fluorine-containing gas fire extinguishing agent on the thermal runaway propagation of the battery is mainly reflected in cooling and extinguishing the flame.The release of the fire extinguishing agent can reduce the peak temperature of the thermal runaway battery by more than 100°C,and the flame can be extinguished within 3 s at the fastest.And no re-ignition occurred.The effect of a fire extinguishing agent is related to its amount and type.The higher the amount of the fire extinguishing agent,the better the suppression effect,which is mainly manifested in the lower peak temperature of the battery,the less number of batteries that have thermal runaway,and the faster the fire extinguishing.All types of fire extinguishing agents can effectively extinguish the battery fire.BTP and FK-5-1-12 have the best cooling effect and fire extinguishing performance in the inhibition of battery thermal runaway propagation.The experimental results are consistent with the theoretical analysis results.The release of fluorine-containing gas fire extinguishing agents will significantly increase the concentration and output of irritating gases,mainly SO₂,accounting for more than 90%of the output.Based on the experimental test and theoretical analysis,the calculation model of cooling performance of fluorine-containing gas fire extinguishing agent is established,and the cooling effect of fluorine-containing gas fire extinguishing agent on the lithium-ion battery is quantitatively evaluated.The research results show that the cooling effect of fluorine-containing gas extinguishing agents are mainly affected by the basic properties of materials and working conditions parameters in the release process.Based on the dimensionless analysis and combined with experimental data,physical parameters and release parameters of the extinguishing agent,the calculation model of cooling performance is established,and the reliability of the model is verified by experiments.The cooling effect of various fire extinguishing agents in the thermal runaway propagation inhibition experiment of lithium-ion batteries is evaluated.The results show that the cooling performance of FK-5-1-12 and BTP is higher,which is consistent with the experimental results.