Study On Combustion And Explosion Hazard Of Large Size Ternary Lithium Battery Under Low Pressure

In order to scientifically evaluate the thermal disaster risk of large format hard shell lithium ternary batteries under normal/low atmospheric pressure,this thesis established a lithium battery thermal combustion and explosion experimental platform,and studied the thermal runaway temperature,thermal runaway heat,vent gas,and vent gas explosion characteristics in low atmospheric pressure environments.The main contents are as follows:（1）It is found that the opening temperature drop of safety valve（35）T_v↓and the critical temperature of thermal runaway T_TRobviously increase with the decrease of air pressure,and the peak temperature of thermal runaway T_peak obviously decreases with the decrease of air pressure.When the atmospheric pressure decreased from 101 k Pa to 21 k Pa and at 100%SOC,（35）T_v↓increases from 5.6℃to 9.6℃;at 60%SOC,（35）T_v↓increases from 5.7℃to 9.1℃;at30%SOC,（35）T_v↓rises from 5.2℃to 6.5℃.Similarly,the T_TR and T_peak is also correlated with changes in ambient air pressure.（2）A thermal model of a large format ternary lithium battery with radiation convection heat dissipation was established.The low pressure environment has a significant impact on the thermal runaway heat characteristics.During the thermal runaway process of the sample battery,the total heat output is Q_hpro=12.88×10⁵ J,and the total heat dissipation is Q_hdis=6.60×10⁵ J.The heat dissipation accounts for 51.24%of the total heat output;the theoretical calculation accuracy of thermal runaway peak temperature for lithium battery thermal model is relatively high,with theoretical calculation value of T_peak^thro=811.9℃and experimental value of T_peak=813.9℃;as the ambient pressure decreases,the convective heat transfer coefficient h decreases,resulting in a decrease in the heat lost by the heating plate to the environment and an increase in the heat transferred to the battery body.（3）It is found that the total amount of battery vent gas V_g and the vent rate s_g increase significantly with the decrease in pressure,low atmospheric pressure environments significantly affect thermal runaway vent gas characteristics.When the atmospheric pressure decreased from 101 k Pa to 21 k Pa and at 100%SOC V_g increases from 44.13 L to 55.01 L;at60%SOC,V_g increased from 27.87 L to 33.50 L;at 30%SOC,V_g increased from 9.87 L to16.38 L;at 100%SOC,the maximum value of s_g increased from 10.33 L/s to 13.92 L/s;at 60%SOC,the maximum value of s_g increased from 6.11 L/s to 13.69 L/s;at 30%SOC,the maximum value of s_g increases from 8.07 L/s to 13.20 L/s.Similarly,the vent gas component is also correlated with changes in ambient air pressure.（4）It is found that the risk of combustion and explosion of lithium battery vent gas decreases significantly as the air pressure decreases,the low atmospheric pressure environment significantly affects the characteristics of thermal runaway vent gas explosions.When the atmospheric pressure decreased from 101 k Pa to 21 k Pa,the lower explosion limit increases from 6.57%vol to 6.85%vol,and the upper explosion limit decreases from 40.04%vol to 38.27%vol,indicating that the explosion limit range of vent gas decreases as the ambient pressure decreases;when the atmospheric pressure decreased from 101 k Pa to 21 k Pa,the maximum explosion overpressure decreases from 0.653 MPa to 0.152 MPa;the maximum explosion index decreased from 9.04 m·MPa/s to 4.03 m·MPa/s.This article comprehensively reveals the thermal runaway thermal characteristics and vent gas hazard characteristics of lithium batteries during the disaster process at constant and low pressure.The research results can provide experimental and theoretical support for the safe application of lithium battery products in low pressure environments.