The Influence Of Cycling Conditions On Thermal Runaway Characteristics Of Lithium Batteries Under Different Pressures

For civil aviation lithium-ion batteries used in aircraft,more and all-electric aircraft development and application.By independently designing experimental devices and platforms for researching thermal runaway characteristics of lithium batteries,the study on the thermal runaway characteristics of lithium batteries under different pressures under cyclic conditions are conducted to ensure the safety or disaster prevention and control of lithium ion batteries under aerospace conditionsIn this dissertation,the 18650 lithium-ion battery is used as the test sample,and the thermal runaway experiments of lithium-ion batteries under different pressure environments of 95 kPa,60kPa,and 20 kPa are carried out by the controlled variable method.The study includes two aspects:(1)The influence of the number of cycles on the thermal runaway characteristics of lithium batteries under different pressures.(2)The influence of cycle rate on thermal runaway characteristics of lithium batteries under different pressures.The experimental results show that:(1)As the number of cycles increases,the gas release and thermal runaway ignition time diminishes,the flame spray intensity increases,and the combustion time becomes longer.The thermal runaway surface temperature,maximum surface temperature and flame temperature diminishes as the number of cycles increases.In addition,the change in the resistance and voltage of the lithium battery during thermal runaway also shows obvious regularity.The fresh lithium battery resistance has a significant peak before the thermal runaway,and the voltage appears on the platform,but when the number of cycles reaches 20 times,the resistance It suddenly rises to the maximum when the thermal runaway is on fire,the voltage drops directly to 0V,and the resistance peak increases with the number of cycles.As the environmental pressure decreases,the lithium battery with different cycles gas release and thermal runaway ignition time is diminished,the flame spray intensity is weakened,and the combustion time is reduced.(2)As the cycle rate increases,the gas release and thermal runaway ignition time diminishes,the flame spray intensity is increased,and the combustion time becomes longer.At the same time,during the thermal runaway,the thermal runaway surface temperature,the maximum surface temperature and the flame temperature decreases as the cycle rate increases.In addition,the change in the resistance and voltage of the lithium battery during thermal runaway also shows obvious regularity.The cycle rate of 0.5C lithium battery resistance before the thermal runaway shows a significant peak,the voltage appears on the platform,and the resistance 1.5C cycle rate lithium battery suddenly rises to the maximum when the thermal runaway fire occurs,and the voltage drops directly to 0V,the peak value of the resistance increases as the cycle rate increases.As the environmental pressure decreases,the lithium battery with different cycle rate gas release and thermal runaway ignition time is diminished,the flame spray intensity is weakened,and the combustion time is reduced.(3)We collected the voltage capacity data of the lithium battery during the cycle,and analyzed the cycle characteristic curve of the lithium battery during the charge and discharge process.It was found that as the number of cycles and the cycle rate of the lithium battery increase,the lithium battery reaches the cut-off voltage without reaching the standard capacity.The capacity loss is obvious,the cathode material and anode material of the lithium battery are lost,and side reactions occur.These changes make the lithium battery significantly reduce the safety during the cycle,it shows obvious regularity during the thermal runaway process.