Simulation And Research On Thermal Runaway Of Lithium Ion Battery Based On COMSOL

Influenced by the skyrocketing booming of vehicles throughout our country,the automobile industry has varied to be over-dependent on oil,resulting in multiple negative impacts,among which environmental pollution and energy crisis have become the main problems facing our country.Aiming to alleviate the current problems,the country has formulated strict emission standards on the one hand,and vigorously promoted the development of new energy vehicles,especially new energy pure electric vehicles on the other.Lithium battery is one of the irreplaceable core technologies of pure electric vehicles,so improving its economy and practicability has undoubtedly attracted much attention.Li-ion battery has unparallelly evolved into the primary choice of energy source for pure electric vehicles due to its superior comprehensive performance and huge development potential.However,as more and more safety accidents of pure electric vehicles occur,it shows that the thermal safety of lithium ion batteries seriously affects the use and development of electric vehicles.Thermal safety problems in the use of pure electric vehicles are mainly caused by improper operations such as extrusion,collision and overcharge of lithium ion batteries,which lead to thermal runaway of lithium ion batteries under abuse conditions.Therefore,a fundamental understanding of the performance characteristics of lithium ion batteries under thermal abuse conditions is helpful to study and predict the thermal behavior of the batteries,and provides effective and reasonable suggestions and reference opinions for improving the thermal management design and optimal control of lithium ion batteries,which is of great significance to the development prospects of new energy vehicles.In this paper,the structure and working mechanism of the ternary lithium ion battery are analyzed,the heat generation equation of the lithium ion battery is elaborated in depth,and the causes of thermal runaway of the battery are analyzed.Its basic characteristic parameters can be generated with the aid of a panel of routine experimental tests,combining with numerical simulation software--COMSOL.The established electrochemical-thermal coupling model of lithium ion battery verifies the accuracy of the model.On the basis of this model and thermal runaway equation,a mathematical and physical model of thermal runaway is established.The internal reaction mechanism of thermal runaway of lithium ion battery under high temperature,internal short circuit and overcharge conditions is analyzed by COMSOL simulation method.The thermal behavior of battery under high temperature is verified by experiments.The analytical formula is deduced for the acupuncture short circuit condition,and the rationality of the analytical formula is verified.As is illustrated from a host of researches,high temperature environment is the cause of thermal runaway of lithium battery,and side reaction is the direct factor of thermal runaway.At the same time,the convective heat transfer coefficient will gradually increase with the increase of temperature,and the initial temperature of the battery will also increase.In addition,the shorter the time for thermal runaway of lithium ion battery,the higher the temperature.The sharp change of voltage and current in internal short circuit causes a large number of heatinduced side reactions to occur in the battery,resulting in thermal runaway.Changing the needling position and lithium batteries with different needling radii,it is found that the shorter the short circuit position occurs in the upper part of the battery and the smaller the needling radius is,the more severe the side reactions of the lithium batteries are and the higher the temperature peak value is.When overcharging a lithium battery,the longer the overcharge time is,the more severe the voltage mutation is.At the same time,it is found that changing the position of the tab has a certain effect on the uniformity of the battery's electric change voltage and temperature.The analytic expression of short-circuit temperature of acupuncture is derived by Green's function method.It is reflected after certain comparision with simulation outcomes,the analytic expression can reasonably and accurately predict and judge the altering characteristics of distinct acupuncture positions and times.