Application Of Phase Change Material In Thermal Management Of Lithium Ion Power Battery

Faced with the pressure of energy crisis and environmental pollution,new energy vehicles have been extensively researched and developed,in which electric vehicles are the representation.Whether the heat dissipation of lithium ion power battery is sufficient or not and whether the temperature distribution is uniform will directly affect the service performance and cycle life of battery,thus affecting the performance of electric vehicle.Compared with traditional cooling systems such as air cooling and liquid coolling systems,phase change material cooling has become a promising cooling method because of its advantages such as high latent heat,high heat dissipation efficiency and no need to consume extra pump power.Therefore,the research on PCM cooling of lithium batteries is of great significance to the progress of thermal management technology of power batteries.In this paper,25-parallel 18650 lithium battery module is researched by means of simulation and experiment.We study the thermal state of PCM cooling lithium battery module under different working conditions.The simulation analysis and optimization of the influence law of PCM cooling lithium battery module on heat dissipation performance are carried out,which provides some ideas and basis for the application of PCM in thermal management of power battery packs.The main research contents are as follows:(1)Theoretical study on heat generation of lithium batteries and establishment of heat generation rate model of individual battery.The heat generation mechanism and the mathematical formulas for calculating the heat of each part are analyzed theoretically.The internal resistance characteristics are tested by HPPC.Based on Bernardi’s theory of heating rate,the UDF program of heat source is compiled.(2)Research on simulation method of PCM cooling lithium battery module.Geometric model and mathematical model are established.(3)Experimental study on PCM cooling lithium battery module.The paraffin/expanded graphite composite PCM was prepared and its thermophysical parameters were tested.We build a charging and discharging test bench of PCM cooling lithium battery module and carry out some tests at different operating conditions,and obtain the temperature rise curves at different measuring points of the battery module.(4)According to the measured thermal physical parameters,the corresponding settings were carried out in Fluent.The 1C~5C discharge was simulated at 5℃,20℃and 35℃.The heat dissipation of PCM cooling lithium battery module was analyzed.The simulation results were compared with the experimental results to verify the correctness of the simulation model.(5)Simulation study on heat dissipation performance of PCM cooling lithium battery module.The influence of battery cell spacing,battery arrangement,PCM thermal conductivity and foam metal porosity on the heat dissipation of battery module is explored,so as to provide ideas for matching of PCM and reasonable design of battery modules.At last,the difference of heat dissipation of lithium battery module between PCM cooling and air cooling under different working conditions was studied.