Study On Fire Safety Characteristics Of Thermal Runaway Extrusion Of Ternary Lithium Battery

The fire safety accidents of new energy electric vehicles caused by the abuse of lithium battery emerge one after another,which greatly damages the safety of people’s life and property.Vehicle collision will lead to mechanical abuse when lithium battery monomer is squeezed.Collision is a common accident in real vehicle conditions,so it is extremely important to study the performance change of lithium battery after extrusion.Ternary lithium battery is a high quality power source,but the existing research object is mainly square shell lithium iron phosphate battery and18650 cylindrical lithium battery,and the research object is mainly structural strength characteristics,lack of safety characteristic parameters.Mastering the variation rule of safety characteristic parameters of ternary lithium battery after extrusion will fill the gap of safety protection research of lithium battery and provide guidance for manufacturing and upgrading of lithium battery.In this study,ternary soft-pack lithium battery was used as the research object,and the mechanical loading method of three-point bending was adopted to carry out the extrusion experiments under different shapes of extrusion head,different extrusion positions and different initial state of charge(SOC)conditions.The main safety characteristic parameters such as temperature,voltage,capacity and internal resistance were collected by extrusion experiment of lithium battery under different conditions.The influence of different extrusion conditions on the safety characteristics of lithium battery was obtained through comparative analysis.The more sharp and narrow the extrusion head shape,the earlier the temperature surge of lithium battery,the higher the temperature surge,the greater the capacity loss,the greater the increase of internal resistance;The closer the extrusion position is to the bottom edge of lithium battery,the higher the temperature rise will be,and the more likely thermal runaway will occur.The closer the extrusion position is to the pole ear,the more capacity loss and internal resistance will be.The higher the SOC of lithium battery is,the more likely the thermal runaway occurs,the greater the voltage drop,the greater the capacity loss,the greater the internal resistance value.Scanning electron microscope(SEM)was used to observe the morphology of anode and cathode materials of lithium battery after extrusion,and the morphology change law of anode and cathode materials of lithium battery under the above extrusion conditions was compared.Based on the theory of one-dimensional electrochemical thermal reaction of lithium battery,three-dimensional solid heat transfer and solid mechanics,the thermal simulation and stress simulation models of terpolymer lithium battery were established based on COMSOL software platform,and the temperature change and stress change simulation of lithium battery under different extrusion conditions were carried out.The simulation results show that the temperature and deformation of lithium battery after extrusion are in good agreement with the actual extrusion experiment.In this paper,the thermal runaway fire safety characteristic parameters of lithium battery under different extrusion conditions are obtained,which has very important guiding significance for the production and manufacture of lithium battery monomer and lithium battery box and the design of lithium battery management system.