Heat Transfer Performance Of Lithium-ion Batteries For Electric Vehicles Based On Immersion Cooling

Since the targets of "Carbon Peaks" and "Carbon Neutral" are proposed,new energy vehicles are gaining attention.Lithium-ion batteries,as the main power component of electric vehicles,have a crucial impact on the distance travelled,safety and operating characteristics of the vehicle.When an electric vehicle is in motion,the lithium-ion battery will emit a large amount of heat energy,causing the temperature of the battery pack to rise sharply.If the battery pack is not dissipated and cooled in time,the high temperature environment will have a great negative impact on the performance and service life of the battery,and may even lead to spontaneous combustion and explosion due to thermal management failure.Therefore,a reasonable and effective thermal management method for battery plays a significant role on insuring the performance of electric vehicles and batteries.This paper is based on the research of submerged cooling lithium-ion battery system,and the main content is as follows.(1)The studied battery test platform was built.The internal resistance of the battery was experimentally tested at an ambient temperature of 30°C.The internal resistance of the battery increased as the depth of discharge and discharge rate increased;the temperature rise of a single battery was tested at different discharge rates,and the temperature of the battery increased as the discharge rate increased;the characteristics of battery in 1C discharge rate was tested at different ambient temperatures,and the maximum temperature rise and maximum temperature difference of the battery gradually increased as the ambient temperature decreased.(2)Based on the experimental test data,the physical parameters of the battery were calculated,the heat source program of the battery was compiled.The temperature field of the single battery at different discharge rate is simulated and analyzed,and the simulation results are consistent with the test results.When the battery is fully discharged at a 3C rate,the temperature of the battery has exceeded 48°C,which exceeds the safe operating temperature range and therefore requires heat dissipation.(3)Experimental studies of single Li-ion batteries under forced air cooling and submerged cooling conditions were carried out.The results show that submerged cooling can maintain the maximum battery temperature and temperature fluctuations within a safe range;visualization experiments show that the bubbles generated by boiling intensify convective heat transfer and thus carry away more heat.(4)The submerged cooling method was analyzed and designed,and then the experimental system components were calculated and selected.Firstly,the dissipation experiment of the battery pack under natural convection conditions at different discharge rates was study;the experiments on the 100% submerged battery pack at different rates were conducted to analyze the temperature rise characteristics of the battery pack;the temperature change of the battery pack under 2C discharge conditions at different submergence heights was studied,and the results show that the maximum temperature and the maximum temperature difference of the battery pack gradually decrease with the increase of the submergence height;the cooling performance of the coolant SF33 was analyzed of the battery pack under 2C continuous charging and discharging conditions,and the results show that the coolant SF33 has good heat dissipation effect.