Study On Thermal Runaway Of Typical Lithium-ion Battery

With the rapid increase in the use of lithium-ion batteries and the occurrence of safety accidents,their safety issues are not only more concerned,but also drag on the further promotion and application of lithium-ion batteries.On the one hand,ithium-ion batteries are dangerous because they have a high specific energy.On the other hand,when the battery is exposed to external high-temperature heat sources or short-circuited by itself,complex chemical reactions occur inside the battery,and a large amount of thermal energy and explosive mixture of gases will be quickly released,which is prone to battery fires and even explosions.Although the safety of lithium-ion batteries has been improved continuously in recent years,it is still difficult to avoid explosion safety accidents due to its inherent "energy-bearing" characteristics under the conditions of external abuse.Therefore,it is of great theoretical significance and practical value to study the thermal runaway law of lithium-ion batteries,to clarify the mechanism and rules of thermal runaway induced by lithium-ion batteries,and to grasp the changing characteristics of characteristic parameters in the process of thermal runaway,which will further enhance the intrinsic safety of lithium-ion batteries and establish efficient control methods for thermal runaway of lithium-ion batteries.The main contents and research results of this thesis include:Firstly,a test platform suitable for the study of the thermal runaway rule of lithium-ion batteries is designed.The platform mainly consists of the explosion-proof laboratory,the battery thermal runaway device,the battery heat runaway trigger device,the testing instrument group of the parameter of battery thermal runaway process,the safety and health protection equipment,etc.It can create different trigger conditions to cause thermal runaway of lithium-ion batteries.The temperature and pressure parameters in the thermal runaway process and the gas products after the thermal runaway can be collected to simulate the thermal runaway process of small batches of lithium-ion batteries.Secondly,the influence of charged state and ambient atmosphere on the thermal runaway of lithium-ion batteries was studied by using the designed test platform of heat runaway rule of lithium-ion batteries.The results show that the thermal runaway of lithium-ion batteries is divided into three stages: the temperature of one battery continues to rise,then the initial burst response phenomenon occurs when the cathode pressure relief valve of two batteries is ruptured,at last the batteries explode.The initial detonation response temperature is about 170~190?.Under the same environmental conditions,after the decomposition of the solid electrolyte interface film,the chemical reactions inside the batteries are different,so that the thermal runaway of battery with more charge is more serious.The temperature at which a lithium-ion battery ignites decreases as the state of charge of the battery increases.The environmental atmosphere has little effect on the thermal runaway temperature of the lithium-ion batteries,but it has a great influence on the amount of gas generated by the thermal runaway of the lithium-ion batteries.The low explosive limit of the thermal runaway gas of the lithium-ion batteries decreases as the state of charge increases.The content of carbon dioxide in the gas released by lithium-ion batteries is the most,which accounts for 30%~40% of the total volume of the gas product,followed by carbon monoxide and methane.Thirdly,using the designed thermal runaway law test platform of lithium-ion battery,the effects of external heat source,environment and contact mode on the thermal runaway propagation of lithium-ion batteries were studied.The results show that in the presence of external heat sources,all the low-capacity cylindrical 18650 batteries in the battery pack are thermally out of control.However,in the absence of external heat sources,whether in a closed environment or an open environment,the heat generated by a single battery thermal runaway is not enough to cause the thermal runaway of the battery pack to spread.