Study On The Thermal Behavior Of Lithium-Ion Battery Cells And The Optimization Of Module Thermal Management

Due to the global energy shortage and the need for environmental protection,the development of electric vehicles has become a recognized trend in the automotive industry.As the core power source of electric vehicles,lithium-ion power batteries will directly affect the reliability of battery systems,which will have an important impact on the safety performance of electric vehicles.Research on the thermal behavior of lithium-ion battery cells and the optimization of module thermal management will improve the reliability of the battery work process,and thus ensure the safety of the battery system.Based on COMSOL Multiphysics software,this paper simulates the thermal characteristics of lithium-ion battery cells and modules under certain normal operating conditions and thermal runaway conditions,and combines experimental data analysis to verify the accuracy of the model.The specific content includes the following three parts:Based on the battery test,the 26 Ah single-package lithium-ion battery was subjected to charge and discharge test,capacity decay test and constant temperature test.The test results show that the battery will appear in the charging and discharging process for three periods.The battery voltage in the middle platform is the most stable and the high-rate charging and discharging will shorten the battery in the stable platform period.When the battery is charged and discharged 2500 times in the specified way,the capacity will be reduced to 80% of the rated capacity;the battery operating temperature will seriously affect the discharge capacity of the battery,and its capacity will be reduced by 30% when the operating temperature is-20 °C.The thermal runaway model of 26 Ah single soft pack battery was established,and the triggering thermal abuse trigger simulation of lithium-ion power battery was carried out.The variation of the internal active material of the battery during the thermal runaway process of acupuncture and the acupuncture radius on the thermal runaway production of the battery were studied.The effects of heat and the accuracy of the model are verified based on acupuncture experiments.It is found that the amount of negative electrode material in the battery is reduced by 50% during the thermal abuse of lithium-ion power battery.The main source of heat is the heat generated by the decomposition of the internal active material at high temperature;the radius of the needle is within 3mm,and the radius is smaller,the greater the internal resistance,this will directly lead to an increase in the heat production rate of the acupuncture point,which in turn leads to an increase in the average temperature of the battery.Based on the single-package lithium-ion battery model,considering the feasibility of the experimental verification model,the 18650 battery module is taken as the research object,and the thermoelectric coupling model of the lithium-ion battery module is established.The charge and discharge rate and liquid are analyzed by using PCM(Phase Change Material)and graphite as filling materials.The influence of the cold flow and the number of liquid-cooled tubes on the temperature of the battery module;the use of acupuncture to trigger the thermal runaway of the battery,to explore the effect of the filling material on the thermal runaway propagation of the battery module;combined with the thermal runaway test data of the battery to verify the accuracy of the model;Based on the proven thermal runaway model of the battery module,the parameters of the battery filling material were changed to study the effect of the filling material on the thermal runaway propagation of the battery.Further optimize the battery thermal management solution.The results show that the filling material and the number of rows of tubes have a great influence on the temperature rise of the normal module of the battery;the optimal number of liquid-cooled tubes is 8 when the filling material is graphite;the PCM material can control the thermal runaway propagation time to 46s/piece;using 30% of the foam metal as a battery filling material will ensure the maximum safety of the battery while reducing the battery module temperature.Based on the acupuncture triggering method,the thermal runaway model of the battery cell is established and verified.Based on the Single cell research,a new thermal management scheme based on the combination of filler material and liquid cooling is constructed.The best effect is achieved when the mass fraction is 30% foam metal composite material as the battery filling material.While controlling the temperature rise of the battery under specific normal conditions,the total runaway time of the thermal runaway in the module is controlled within 63 s.