Study On The Thermal Characteristics Of Soft-packed Ternary Material Lithium-ion Batteries During Discharge

With the increasing emphasis on environmental protection in the world,new energy electric vehicles have been vigorously promoted by various countries.The electric vehicles of China have started industrial production,and soft pack ternary lithium-ion batteries have become the preferred power battery.In this paper,26 Ah flexible packaging ternary lithium-ion battery is taken as the research object,and the thermal characteristics of the battery discharge process are studied.The Hybrid Pulse Power Characterization(HPPC)method was used to obtain the internal resistance of the battery at different temperatures(-10?~50?)and different depths of discharge.The internal resistance of the battery was fitted to the temperature and depth of discharge.alternative relation.Through the adiabatic temperature rise test,according to the battery heat balance equation in the discharge process to calculate the heat generation rate under different discharge rates,analysis of battery heat rate changes.The rate of heat generation of the battery during the discharge shows a certain degree of fluctuation with the depth of discharge;at the time of small rate discharge,there are two minimum values,which are near 45% DOD and 90% DOD;and one small during large rate discharge.value.The first minima is the result of the combined effect of internal resistance and entropic heat,in which the entropy heat behaves as an endothermic reaction,resulting in a lower rate of heat generation in the medium of the small rate discharge;the second minimum value is due to the internal phase of the battery.Endothermic reactions change,resulting in lower heat generation rates.Through the 0.25 C rate discharge test and based on the irreversible thermal subtraction method,the entropy heat coefficient change curve of the battery was calculated.Using a high-precision digital voltmeter to test the open-circuit voltage changes of the battery at different discharge depths and different ambient temperatures(-10°C,10°C,30°C,and 50°C),the experimental value of the entropic heat coefficient was obtained,and the calculated and experimental values were obtained.comparing.The entropy-thermal coefficient of the lithium-ion battery in the soft pack is constantly changing during the discharge process.The overall trend of "enlargement-decrease-increase-reduced-re-increasing" oscillations appears,and two minimum values appear.At 25% to 65% DOD and 80% to 90% DOD,is the main factor causing battery temperature fluctuations.Based on the internal resistance and the change curve of the entropy heat coefficient,a heat generation model with a constant change of the heat generation rate over time was established.The software BDS and Star-CCM were used to simulate the temperature changes at different discharge rates.The simulation results reproduce the non-linear changes in temperature and heat generation rate during battery discharge.Comparing the three-dimensional simulation results with the thermal imaging test,it can be seen that as the discharge magnification increases,the temperature gradient of the battery gradually increases,and the temperature gradient of the battery surface becomes closer to the tab;the battery temperature gradient increases;as the discharging process progresses,the battery maximum temperature gradually shifts from the positive and negative ears to the core center position.