Study On The Response Characteristics Of Soft Pack Batteries Under Extrusion Conditions And Battery Performance After Damage

In recent years,a number of electric vehicle safety accidents have occurred at home and abroad.In the collision-induced electric vehicle fire and explosion accidents,often more serious damage to people and property.The reason for this is the thermal runaway of the battery components inside the electric vehicle.Therefore,it is crucial to study the safety of the battery component scale.In this paper,we will study the response characteristics of the high rate lithium cobalt-acid battery used in our HRT fleet under extrusion conditions.Moreover,nowadays,after the collision of electric vehicles,all battery cells in the battery pack are scrapped regardless of whether they are damaged or not and the degree of damage,which causes great waste and industrial pollution.In this paper,we conduct discharge tests on batteries within a certain degree of damage to study whether the damaged batteries can continue to be used and the influence of the degree of damage on the temperature characteristics of the batteries during discharge.In this dissertation,quasi-static squeezing experiments were first conducted on the soft pack battery,and the squeezing test was repeated on the same SOC state battery to verify the repeatability of the squeezing test on this soft pack battery.The results indicate that the changes of load,temperature and cell data are basically the same for the three experimental groups,which proves that the characteristics of this type of battery can be characterized by the experimental study of a small number of cells.After that,different squeezing speeds were set for squeezing tests on soft pack batteries,and the higher the squeezing speed the higher the peak load of battery failure was obtained,revealing the effect of squeezing speed on the mechanical response of the battery under longitudinal loading.Finally,quasi-static squeeze tests were set up for different charge state batteries,and the higher the SOC state,the higher the peak temperature of the battery at thermal runaway,in the radial squeeze experiment of the soft pack battery.However,the higher the SOC state,the higher the peak load of the battery within a certain SOC range,the larger the failure displacement boundary of the battery,which means that it is more difficult to reach the failure boundary of the battery,and to some extent the increase of SOC makes it more difficult for thermal runaway to occur in this battery.According to the above quasi-static squeeze test of soft pack batteries in different SOC states,the experimental results show that thermal runaway does not occur immediately after the battery is squeezed,and battery failure occurs only after a displacement of more than 50% of the thickness in each state.The data show that the temperature rise of the low-damaged battery is similar to that of the normal battery during discharge,while the peak temperature of the high-damaged battery is too high when discharging at a high rate,and 20% of the damaged battery cannot complete the 15 C discharge condition.After changing the temperature of the thermostat to 50℃ and 0℃,we got that the high temperature environment will amplify the effect of the damage degree,while the low temperature environment is the opposite.A hybrid pulse test was performed on the damaged battery to construct the equivalent circuit model of the battery.The polarization internal resistance of the highly damaged pouch cell is slightly higher than that of the normal battery,and the ohmic internal resistance is substantially higher than that of the normal cell.This phenomenon explains that the higher peak temperature of the damaged battery under the discharge test is more due to the increase of the ohmic internal resistance.In this paper,by performing performance tests on batteries with different levels of damage,the results show that low-level damage batteries can continue to be used.The establishment of an equivalent circuit model of the damaged battery and the identification of parameters explain the reason why the peak temperature of the highly damaged battery is too high in the performance test.