Experimental Study On Thermal Characteristic Of Power Battery And Optimum Design Of Air Cooled Structure

In recent years,with the development of economy and the acceleration of industrialization process,the speed of energy consumption is increasing sharply,and the environmental pollution is becoming more and more serious.As an important method to solve this problem,electric vehicles have attracted widespread attention.As one of the three core modules of electric vehicle,power battery is the key to developing electric vehicles.Lithium-ion battery has become the preferred power source for high-performance electric vehicles because of its high operating voltage,fast charging and discharging,high capacity density,low self-discharge rate and long service life.In the actual use process,especially in the case of high discharge current,lithium-ion battery will release a lot of heat,resulting in excessive temperature and local temperature difference,which will affect the normal operation of batteries,and even cause combustion or explosion accident.Therefore,it is very important to improve the safety of battery packs by using reasonable battery thermal management technology.Air-cooled system has simple structure,light weight and low price and it is widely studied.In this paper,the air-cooled system is explored by combining experimental and computational fluid dynamics（CFD）.Firstly,the charging and discharging platform for lithium-ion battery is built,and the performance of the battery during discharging is tested,such as voltage,capacity,internal resistance,surface temperature,etc.According to the voltage change and discharge capacity of the battery in the discharge process,the battery with similar performance is selected to form the battery pack.According to the test results of the internal resistance of the battery,the battery can be regarded as a constant body heat source.The reliability of the heat generation model is further verified by analyzing the change of the battery surface temperature in the discharge process.Secondly,the experimental platform of lithium iron phosphate battery pack and air-cooled structure are built.The temperature changes of the battery pack under different convection conditions and different discharge conditions is tested.By comparing the temperature change of battery pack under natural convection and forced convection,it can be seen that forced convection can effectively depress the maximum temperature and local temperature difference of battery pack.The model of the battery pack is constructed,and the temperature change of the battery pack in the air-cooled structure is simulated by CFD software.It is found that the experimental and simulation results are very similar,which verifies the reliability of the model.Finally,on the basis of the model mentioned above,the air-cooled structure is optimized by changing the battery spacing and the air velocity.It is found that the temperature field of the battery pack and the air flow field in the battery box are greatly improved when the batteries are arranged with unequal spacing.The spacing of the battery decreased from the inlet to the outlet in turn.It has the lowest temperature and the smallest local temperature difference when the widest spacing is4 mm and the tolerance is 0.2 mm.When the air speed reaches 3 m s^-1,the maximum temperature and local temperature difference of the battery have reached the requirement of lithium iron phosphate battery pack.In summary,the optimized air-cooled structure can depress the maximum temperature and local temperature difference of the battery,and all meet the requirements of lithium iron phosphate battery pack.