Investigation On Heat Dissipation Performance Of Vehicle Lithium-ion Battery Module With Phase Change Material And Liquid Cooling

In order to solve the global energy crisis and environmental pollution problems,electric vehicles have been vigorously promoted because of its advantages of low energy consumption and zero emissions.Lithium-ion battery is the core of electric vehicles,and the performance of battery directly affects the driven distance and the safety performance of electric vehicles.If the heat generated by battery discharge cannot be transferred in time,the battery temperature will rise rapidly.The performance and life of the battery will decline sharply,which even causes thermal runaway and explosion.Therefore,the establishment of an efficient,safe,and reliable battery thermal management system is of great significance for solving the electric vehicle mileage concerns and safety issues.Firstly,this paper researches the basic structure,heat generation mechanism,heat transfer characteristics and thermal calculation model of lithium-ion batteries.Taking18650 Li（Ni Co Mn）O₂ as the research object,the internal resistance characteristics of the battery under different operating conditions are tested,and the internal resistances of the battery under different state of change（SOC）are obtained.Based on the battery heat generation rate model proposed by Karimi,the per unit volume heats of the battery at different discharge rates are obtained.A single cell mesh model is established by Hypermesh,the temperature distribution of the battery during natural convection cooling is obtained by CFD（computational fluid dynamics）,and the reliability of the battery thermal simulation model is verified by comparing the simulated with experimental values of the maximum temperature of battery.Subsequently,the PCM is used to cool the single battery,and the maximum temperature and temperature difference of the battery are controlled effectively.Secondly,a novel thermal management system is proposed based on paraffin phase change material（PCM）coupled with liquid cooling.A numerical research is conducted by CFD to investigate the effects of the battery’s thermal characteristics at an ambient temperature of 40°C at various flow velocities,channel layouts and fin with different widths.In order to further optimize the heat dissipation performance of the battery module,taking expanded graphite（EG）/paraffin composite as the PCM to investigate the effects of the battery’s thermal characteristics at composite phase change material（CPCM）with different mass fraction of EG.Furthermore,the thermal behavior of the integrated thermal management system（ITMS）in a charge–discharge cycles is analyzed.The result indicates that temperature rise and difference of lithium-ion batteries with ITMS are maintained within a desirable range under low energy consumption at a discharge rate of 3C.Finally,a battery pack thermal management system is proposed based on the battery module with ITMS,and the battery pack’s thermal characteristics at different flow rates and flow path with different in and out modes are analyzed.The result indicates that the maximum temperature and difference of the battery pack are reduced effectively by the staggered entry and exit of the liquid.In addition,the response surface method is used to analyze the effects of the three factors of coolant flow rate,ambient temperature,and the proportion of ethylene glycol in the ethylene glycol aqueous solution on the maximum temperature and difference of the battery pack,the result presents that the alcohol ratio and ambient temperature have significant effect on the maximum temperature of the battery pack.