Study On Electrochemical-thermal Characteristics Of High Specific Energy Lithium Ion Batteries For Vehicles

With the gradual improvement of the performance of new energy vehicles,the specific energy of lithium ion batteries for vehicles is also increasing.The high specific energy battery will generate more heat during charge and discharge,which may affect the battery performance and even cause safety hazards Therefore,it is of great significance to study the electrochemical thermal characteristics of the battery for guide the battery thermal management and battery design.Focusing on the study of the electrochemical thermal properties of lithium-ion batteries,the following research work was carried out in this paper:The 11 Ah lithium-ion battery was tested for capacity calibration,HPPC(Hybrid Pulse Power Characteristic),constant current condition,pulse condition,and electrochemical reaction entropy thermal coefficient.Analyzing the test results,which shows that the battery capacity is greatly influenced by temperature and discharge rate;with the growth of the DOD,the entropy heat coefficient of the battery increases first and then decreases,and reaches the maximum value at 50 % DOD;the temperature at battery center is highest under different test conditions.According to the basic principle of the electrochemical model of the battery,an electrochemical model of the lithium-ion battery was established based on the Comsol software,and then the model was calibrated and verified based on the experiment datas.Compared with the test,there is almost no error in the simulated battery capacity,and the maximum relative error of the voltage is 2.06 %.AT the same time,the electrochemical model can be used to study the electrochemical characteristics of the battery under different conditions via adjusting the temperature correction factor of the relevant parameters.Then the effect of 12 tunable parameters in the electrochemical model on the electrochemical characteristics of the battery was systematic studied using athe calibrated model system.The results shown that: the average current density,the thickness of the electrode,the maximum intercalacable,the initial intercalacable lithium ans the positive particle radius make a great difference in the voltage and capacity about the electrochemical model,while the other parameters have little effect on the battery capacity and just slightly affect the battery voltage.Based on the Comsol software,an electrochemical thermal coupling model for lithium-ion batteries was established and verified using constant current discharge results data obtained at different temperatures and currents test.The results show that the electrochemical thermal coupling model can be used to study the thermal characteristics of the battery under different temperatures and operating conditions.The effect of eight adjustable parameters in the model on the thermal characteristics of the battery was analyzed using the constructed electrochemical thermal coupling model system.The results show that the average current density,convection heat transfer coefficient,the thickness and maximum intercalacable of the cathode have a great influence on the temperature rise of the battery,while the others have little effect on the temperature change of the battery.Among these eight parameters,only the convection heat transfer coefficient of the battery has a greater influence on the isotherm at the end of the discharge of the battery.As the convection heat transfer coefficient increases,the temperature rise of the battery will decrease,but the uniformity of the temperature distribution of the battery will deteriorate.