Thermal Characteristics Of Battery Module Based On Phase Change Material-Aluminum Plate-Fin Composite Heat Dissipation

In recent years,with the advent of the fossil energy crisis,countries have invested funds and optimized policies to lay out new energy tracks,and pure electric vehicles are developing rapidly in this environment,but the main problems facing by pure electric vehicles are short range,high temperature during high rate of charge/discharge and so on.Lithium-ion（Li-ion）battery,as one of the power sources of electric vehicles,its performance is extremely sensitive to changes in temperature.Its normal operating temperature is 20～45℃.Once the temperature exceeds 50℃for a long time,it is easy to cause battery thermal safety problems.If the temperature is below 10℃,especially below 0℃,it will increase the battery DC internal resistance,resulting in battery charging blocked.Aiming at the problems of thermal safety and thermal equilibrium caused by the influence of temperature on battery performance,it is vital to design an efficient thermal management system to ensure the battery to work at the optimal temperature.In this paper,the ternary pouch lithium-ion battery is taken as the research object.Adopting the method of combining experiment with simulation,the composite heat dissipation structure of phase change material（PCM）-aluminum plate-fin was designed.According to the heat generation-transfer mechanism,the DC internal resistance and entropy change coefficient of the battery were obtained based on HPPC and entropy change coefficient experiments,so as to establish the accurate thermal model.And the simulated and experimental temperature rise of the battery cell under different discharge rates was compared to verify the reliability of the thermal model of the battery.Based on the battery cell verification model,three heat dissipation structures of the battery module were designed to compare the heat dissipation characteristics with natural convection,pure phase change,and PCM-aluminum plate-fin composite heat dissipation at 4C discharge rate,so as to obtain the structure with the best heat dissipation effect.On this basis,the heat dissipation effects of different discharge rates and phase change material melting points were analyzed,and the structural parameters were optimized to obtain the best PCM-aluminum plate-fin composite heat dissipation system.The details of the work are as follows.（1）Theoretically analyze the generation-transfer-dissipation law of Li-ion battery,according to the HPPC and entropy change coefficient experiments under different temperature,the DC internal resistance and entropy change coefficient were measured to establish the battery thermal model.The experimental data were compiled into a field function and introduced into STAR-CCM+.The temperature rise of the battery cell at different discharge rates was simulated by CFD,and the accuracy of the thermal model of the cell was verified by comparing the experimental data of temperature rise under the same discharge rate.（2）Natural convection,pure phase change and PCM-aluminum plate-fin composite cooling structure were designed to cool the battery module at 4C discharge rate,and the cooling effect of each cooling structure during discharge was analyzed instantaneously.Then,takingΔT_{ma x}and T_{ma x} of the battery module as indicators,it was concluded that the cooling effect of PCM-aluminum plate-fin composite cooling structure was the best,and its T_max was decreased by 30.2℃and 17.2℃respectively compared with natural convection and pure phase change cooling.（3）On the basis of the composite heat dissipation structure of phase change material-aluminum plate-fin,the temperature distribution trends at the discharge rate of 2C,3C,4C and5C were analyzed.And it was concluded that even at 5C discharge rate,T_max remains in the normal working temperature range of the battery when t<675s.At 4C discharge rate,the influence of different melting points of PCM on the heat dissipation of battery modules was studied.The higher the melting point of paraffin wax,the longer it took to play the role of latent energy absorption.The latent energy absorption of paraffin wax with the melting point of 28℃is the best at the ambient temperature of 25℃.（4）In order to further improve the composite heat dissipation effect of PCM-aluminum plate-fin,the effects of d_pcm,b_fin and s_fin on the heat dissipation of the battery under the same discharge rate were studied with a,ΔT_{ma x} and T_{ma x} as the evaluation indexes.It was found that simply increasing d_pcm was not good for the heat dissipation effect of the battery,and the best heat dissipation effect could be achieved by matching b_fin and s_fin.It is concluded that when d_pcm=8mm,b_fin=7.5mm and s_fin=4 mm,the comprehensive heat dissipation effect of battery module is the best.