Thermal Runaway Characteristics Of Nail Penetration-triggered Lithium Ion Battery Under Different Air Pressure Condition

Based on the widespread use of lithium ion batteries and the safety of batteries in air transportation,,this thesis studied the rules of thermal runaway triggered by penetration of two batteries under different atmospheric pressures through experimental design and independent experimental platform.It can provide further theoretical support for the safety protection in the process of air transportation of lithium ion batteries.In this thesis,four charged states were set as 100%,75%,50% and 25%,and five air pressures were 90 k Pa,80 k Pa,70 k Pa,60 k Pa and 40 k Pa respectively.Under each SOC condition,experiments of needle-triggered thermal runaway were carried out under 5 different air pressure conditions.It was analyzed that the thermal runaway characteristics of 18650 lithium ion battery and pouch lithium ion battery under different air pressure.The results are as follows: In the nail penetration experiment of 18650 type lithium ion battery,(1)With the decrease of SOC,the combustion duration of the thermal runaway stage of battery increases,and the peak temperature also increases correspondingly.When SOC is reduced to 25%,the peak surface temperature decreases by 260℃,and the risk of nail penetration-triggered thermal runaway decreases.(2)With the decrease of ambient pressure,the spark ejecta behavior of nail penetration-triggered thermal runaway is advanced,the combustion duration is reduced,the peak temperature of battery surface is reduced,and the risk of needle-triggered thermal runaway is reduced.When the pressure decreased from 90 k Pa to40 k Pa,the peak surface temperature decreased the most at about 80℃ under 100%SOC condition,and the inhibition effect on thermal runaway was the most obvious.(3)When SOC is high(100%SOC,75%SOC),the voltage sag point is less affected by ambient pressure;When SOC is low(50%SOC,25%SOC),the side reaction heat release rate of the battery is affected by oxygen concentration,and a large area internal short circuit will occur later when the air pressure decreases.Under 25%SOC,the pressure was reduced from 90 k Pa to 40 k Pa,and the point at which the voltage sag occurred was delayed by 3 mm.In the nail penetration experiment of the pouch lithium ion battery,(1)with the decrease of SOC,the combustion time in the thermal runaway process decreases,and the surface peak temperature decreases.When SOC decreases to 25%,the surface peak temperature decreases340℃.(2)When SOC is high(100%SOC,75%SOC),the battery is prone to detonation with the decrease of ambient pressure,and the peak surface temperature tends to rise first.The time point of battery voltage beginning to decline is earlier,and the time point of internal short circuit is earlier,and the risk of thermal control increases.When SOC is low(50%SOC,25%SOC),the peak temperature of battery surface decreases significantly with the decrease of ambient pressure.The decrease of ambient pressure will lead to the slow heating of battery side reaction,the diaphragm reaches the failure temperature later,the time point delay of large area internal short circuit,and the risk of thermal runaway decreases.(3)Compared with 18650 lithium ion battery,the surface peak temperature of pouch battery is lower in the experiment,and it is more significantly affected by oxygen concentration and pressure difference.