Thermal Behavior And Thermal Management Optimization Of Power Battery For New Energy Vehicle

The non-renewability of traditional energy and environmental pollution are urgent problems to be faced at present.At the same time,with the increasing turbulence of the international situation,it has become a major trend for new energy vehicles to replace traditional fuel vehicles.In the development of new energy vehicles,lithium-ion batteries have become the power source of vehicles because of their excellent properties such as high energy density,long cycle life and no pollution.However,the hidden danger of thermal runaway limits the further development of new energy vehicles to a certain extent,so it is of great significance to study the thermal behavior and thermal management of lithiumion batteries.This paper investigates the thermal behavior of new energy vehicle power lithium-ion batteries,the thermal management system and one of the causative factors of thermal runaway,lithium dendrites.Comprehensively consider the coupling effect of temperature,concentration,voltage,current and other physical fields.Through electrochemistry,thermodynamics,heat transfer,fluid mechanics and other disciplines to confirm each other,the main research contents are as follows:For the thermal management system of lithium-ion power battery,the electrochemical model of lithium iron phosphate single battery and the thermal model of battery group are established.The coupled wind field model explores the influence of wind field and physical structure on battery heat dissipation,and analyzes the heat generation and air-cooling characteristics of the battery pack.The air-cooled heat dissipation system of Li-ion battery is optimally designed from the perspective of battery pack arrangement,inter-pack spacing,air speed and ambient temperature,with the goal of lowest maximum temperature and lowest inter-pack temperature difference.The results show that when the battery pack is arranged smoothly and the spacing of the battery pack in Y direction and X direction is 32 mm and 4 mm respectively,the maximum temperature of the battery pack can be controlled within 24 ℃ and the temperature difference can be controlled below 3.2 ℃.In addition,the wind speed is not the greater the better,from the perspective of energy consumption will be controlled under normal operating conditions of the battery within a reasonable temperature range of wind speed is the optimal choice.Taking the lithium iron phosphate power battery pack as the research object,a Z-type air cooling system with non-vertical structure is designed.The heat release and air-cooling heat dissipation model of the battery pack is established,and the heat generation characteristics of the power battery pack during charge and discharge are analyzed.Investigate the effects of inlet/outlet and inter-runner tilt angles,runner width and wind speed on cell pack temperature and optimize cell thermal management solutions.The results show that the best optimal angle between the inlet/outlet and the airflow channel is 19 °,and the maximum temperature and maximum temperature difference of the battery pack are36.86 °C and 2.44 °C respectively.Compared with the conventional Z-type BTMS,the heat dissipation effect is enhanced by 3.4% and 5.8% respectively.Without increasing the power consumption,the heat dissipation performance of BTMS can be improved by adjusting the channel width and inlet wind speed the optimized channel width and wind speed are 2 mm and 4 m/s respectively.Non-vertical structure Z-type BTMS has better heat dissipation efficiency,it takes 1000 s for non-vertical structure Z-type BTMS to drop from 35 ℃ to 33 ℃,while 1200 s for vertical structure BTMS.Under the same conditions,non-vertical structure BTMS cooling can save 17% time.The basic design of this non-vertical structure Z-type air cooling system proposed in this study has a certain engineering value and reference significance for the design of BTMS.Taking lithium dendrite as the research object,which is one of the causes of thermal runaway of lithium-ion battery.The growth model of lithium dendrite in liquid electrolyte is established by phase field equation,and the growth of single dendrite and multiple dendrites is simulated,the effect mechanism of ambient temperature on dendrite growth was analyzed,the effects of different anisotropic strength and diffusion coefficient on dendrite growth were studied,and the growth mechanism of lithium dendrite was summarized.The results show that the dendrite grows faster at low temperature than at high temperature;the greater the anisotropic strength,the faster the dendrite growth;the diffusion coefficient determines the lateral and vertical growth rate of dendrite,and affects the morphology of dendrite.Through the study of the kinetic process and morphology of lithium dendrite growth,it is of certain significance to further understand the thermal runaway of lithium ion battery.