Research On The High Explosion Characteristics And Mechanism Of Commercial 18650 Lithium Ion Battery During Thermal Runaway Under Low Charge State

Lithium-ion batteries(LIBs)have the advantages of high energy density and no memory effect,and are widely used in consumer electronics,power energy and aviation products.However,safety problems such as fire and explosion hinder its large-scale application.Especially in the air transportation accident,LIBs may release toxic substances and combustible gases in the stage of thermal runaway(TR),thus causing explosion hazard to the environment of the passenger cabin,cargo hold or compartment where the LIBs are located.In this thesis,18650 LIBs which are commercially available on a large scale in the market are taken as the research object.Based on the experimental platform of thermal abuse of LIBs,the TR process,combustion and explosion characteristics of different SOC cells are explored,and the influence of micro-induced position is determined by heating experiments at different rates.Finally,the internal structural deformation of the cell caused by TR is determined by non-destructive detection with CT,to deeply analyze the internal mechanism and law of TR and high explosion characteristics of LIBs.The results show that 40%-50%SOC cells show obvious randomness,and 45% SOC cells have the TR difference behavior with shortest time interval and extremely high probability of explosion.Among them,the steel shell of 45% SOC cell which has experienced explosion is generally discolored in a large area,and the color in the bottom area is the deepest and densest.In general,the commercial 18650 LIBs at 45% SOC levels have high TR and explosion characteristics under the existing battery internal structure and differential design level of safety protection.In addition,through analysis,it is found that some inducements lead to some disastrous consequences in the process of TR evolution,including blockage of exhaust passage,cavitation stratification,structural collapse and axial \ radial deviation.Even cells with different deformations show the same characteristics and laws of TR and high explosion under the same heating conditions.In a word,the 45% SOC cell can meet the conditions of continuous gas production and pressurization at the same time during TR,so it can cause blockage of exhaust channel with greater probability,and then make the internal and external pressure difference exceed the bearing limit of external steel shell and cause explosion when having the same heat dissipation design.