Research On Thermal Runaway And Ignition Characteristics Of Lithium Batteries

With the development of my country’s economy and society,energy shortage and environmental pollution have become two major problems that we must pay attention to.Among them,automobiles are a key area that needs to be paid attention to because of the large amount of energy consumption and exhaust emissions.Major countries in the world have focused on the new energy vehicle industry.In recent years,due to my country’s vigorous development,our new energy vehicle industry has also taken the lead in the world.With the popularization and promotion of electric vehicles,news of electric vehicle accidents also frequently appears,which undoubtedly greatly affects consumers’ confidence in electric vehicles.This study focuses on the power lithium-ion battery for vehicles and conducts research through comsol software.Calculated,analyzed the thermal runaway behavior of lithium batteries and the combustion characteristics of PVC materials commonly used in ignition vehicles,and then put forward risk control measures and suggestions for the thermal runaway behavior of lithium batteries.The main research completed in this paper is as follows:（1）The components of the lithium-ion battery and its working principle under normal working conditions are firstly introduced,and then the mechanism of heat generation inside the lithium-ion battery and the heat exchange process with the outside world are analyzed.The triggering factors that cause thermal runaway in lithium batteries and the different thermal runaway processes caused by different factors are summarized.Finally,the calculation method of heat generated by side reactions inside lithium batteries and the generation of gas are introduced.At the theoretical level,it is a theoretical basis for the subsequent puncture of lithium batteries.The modelling provides a clear theory.（2）By establishing the thermal runaway model of the 18650 lithium-ion battery under puncture conditions,the effects of the needle diameter,the puncture depth,the puncture position and the battery’s own charge on the thermal runaway behavior of the battery were studied.The diameter of the needle has no obvious effect on the temperature development trend of the battery,but has a relatively obvious impact on the peak temperature that the battery can reach.The two generally show a negative correlation.When the diameter of the needle is larger,the battery The lower the peak temperature that can be achieved;the penetration depth has a very obvious impact on the development process of thermal runaway of the battery.When the penetration depth is shallow,the temperature of the battery will only increase slightly,and there will be no thermal runaway phenomenon.When the piercing depth exceeds a certain limit,the battery will soon experience irreversible thermal runaway;the piercing position also has no significant effect on the development trend of thermal runaway of the battery,but when the piercing position is lower,the battery can The higher the peak temperature reached;the final state of charge of the battery has a very significant effect on the thermal runaway behavior.（3）The thermal runaway model of igniting PVC materials by puncturing the battery was used to study the effects of different ignition methods,battery puncture at different positions,and separation distance on the overall thermal runaway behavior.The conduction inside the battery pack makes its ignition speed lower than that of the fixed power ignition source,and the energy released by the battery thermal runaway makes its peak heat release rate much greater than that of the fixed ignition source;The closer the position is to the PVC material,the faster it ignites the PVC material and affects its peak heat release rate.The more central the thermal runaway occurs,the higher the peak heat release rate;the distance between the battery pack and the PVC material is It has the effect of promoting ignition within a certain range,but when it exceeds a certain distance,the battery pack cannot ignite the PVC material.（4）The extreme abuse acupuncture model of the battery is constructed through the acupuncture influencing factors of the battery,and the thermal management system is simulated outside the battery.The paraffin and graphene composite phase change material is used as the medium,and the thermal management system is found to effectively reduce the battery The temperature at which thermal runaway occurs,and its peak temperature decreases from 768.32°C to 437.12°C.At the same time,the battery management system of the electric vehicle is designed,and it is proposed to monitor the current,voltage,temperature and charge of the battery in real time,and judge whether the battery is faulty through various data conditions,and run the steps according to the battery management program.,to realize the classification alarm for faults.From the passive safety design,active safety design and intrinsic safety design of the battery,measures to improve the safety of the battery are proposed,which can suppress the occurrence of thermal runaway of the battery from the root cause.