Experimental Research Of Thermal Management Of Li-ion Battery Pack In Pure Electric Vehicles

In recent years,with the development of economic society and the improvement of people's living standards,the car has gradually become a travel essential.Electric vehicles have become the first selection of new energy vehicles with the advantages of zero emissions,low noise,simple structure and high energy efficiency.However,power battery has been the technology bottleneck and it restricts the development of new energy vehicles with the disadvantages of high cost,low energy density,short service life,serious indirect pollution,unsound distribution facilities and many other problems.Lithium-ion batteries have become the dominant power of electric cars for its advantages.However,lithium-ion battery will produce a lot of heat in use,if effective thermal management measures were not taken,the temperature will become too high and uneven,which will have a serious influence on the life and dynamic performance of the battery pack,and even lead to security problems due to high temperature.Therefore,it is particularly important to develop reasonable battery thermal management system and optimize the structure of heat dissipation.In this paper,we take lithium iron phosphate power battery as the research object,describe the mechanism of heat generation and temperature characteristics of the lithium-ion battery,design and assembly the test system,and perform charge-discharge tests under various working conditions.Mainly we change experimental conditions by changing cooling method and discharge rate of the battery pack.Cooling methods include gapless natural cooling,equally spaced natural cooling,naturally cooling with aluminum fins,naturally cooling with copper fins,and so on.The discharge rates are 0.5C,1C,1.5C,2C,2.5C and 3C.By analyzing the maximum temperature location,minimum temperature location and other parameters such as the maximum temperature and minimum temperature,we studied the influence of cell spacing,discharge rate,discharge depth,fin thickness,fin height,fin material on temperature distribution and variation characteristics.The results show that the maximum temperature rise and the maximum temperature difference of the battery pack increase with the depth of discharge.The temperature increases rapidly both in the initial and at the end of discharge process,and in the middle it increases more slowly.The highest temperature of the battery pack locates in the center below the electrodes and the lowest temperature locates in the outer surface of the outside pack,the maximum,minimum temperature position is stable throughout the whole discharge process.For the same structure,the maximum temperature and the maximum temperature difference increase with the increase of discharge rate,thus increasing the difficulty of thermal management.Leaving gaps between cells could not effectively improve the temperature distribution,and will exacerbate the unevenness of temperature distribution to some extent.Installating metal fins between batteries can significantly improve the temperature distribution,and there is an optimum fin height.For the same height,the thicker the fins,the better the thermal management effectiveness,but the battery system will become heavier.Using fin materials of larger thermal conductivity can significantly improve the temperature distribution of the battery pack.