Research On Application Of Composite Phase Change Material In Thermal Management Of Power Battery

In response to the two major world problems of environmental pollution and energy crisis,the development of electric vehicles has become a global consensus.With the rapid development of electric vehicles,people have put forward higher requirements for the safety and battery life of electric vehicles,and the design and development of more efficient and reliable thermal management systems has also become the focus of research in the field of electric vehicles.The battery thermal management system based on phase change cooling has the advantages of energy saving,prevention of battery thermal runaway and excellent temperature control performance,and is considered to be one of the most promising battery thermal management technologies.In this paper,18650 lithium iron phosphate battery pack is used as the research object,and the method of combining simulation and experimental verification is used to analyze and study the heat dissipation,heat preservation and heating functions of the phase change thermal management system of the power battery.First,the structure,working principle,heat transfer and heat generation mechanism of lithium-ion batteries are comprehensively analyzed;HPPC experiments of single lithium-ion batteries are carried out to obtain relevant data and obtain the internal resistance values of batteries under different SOCs through theoretical calculations.The relationship between the battery internal resistance and the SOC is obtained by basic fitting,and the UDF program of the internal heat source of the battery is completed;the thermal physical parameters and internal heat source program of the lithium-ion battery obtained by the comprehensive calculation simulate the discharge process of the single lithium-ion battery.The result is compared with the data of the temperature rise experiment,and the error is found to be small,which verifies the correctness of the heat production model of the single cell and can be used for further simulation analysis.Secondly,seven different composite phase change materials were prepared by adding different proportions of expanded graphite and nanoparticles to paraffin wax,and the effects of different material ratios on the thermophysical properties of composite phase change materials were compared and analyzed.Third,the heat dissipation performance of the composite phase change material to the battery pack is studied through experiments and simulation calculations,and the arrangement between the battery and the composite phase change material,the thermal properties of the composite phase change material,and the heat dissipation of the battery pack when combined with air cooling are analyzed.Impact.Finally,in order to improve the low-temperature performance of the battery,heat preservation design and heat preservation experiments were carried out on the battery pack,and the influence of the type and thickness of the heat preservation material on the heat preservation effect was analyzed.At the same time,the hot air heating and heating were analyzed from the perspectives of heating time and temperature uniformity.The heating effect of rod heating and heating film heating on the battery pack.The research results show that:(1)the increase of a small amount of nanoparticles can further improve the thermal conductivity and phase change latent heat of the expanded graphite/paraffin composite phase change material;(2)appropriately increase the thermal conductivity of the composite phase change material and ensure the surrounding battery Consistent and sufficient amount of composite phase change material is the key to improving the heat dissipation effect;(3)The heat sink designed in this topic can effectively enhance heat dissipation and reduce the local temperature difference when air cooling and phase change cooling are combined;(4)The heat preservation design can effectively reduce The heating time and energy consumption required for electric vehicles to stop and start cold for a short time in a low temperature environment,and the heat preservation conditions can effectively improve the temperature uniformity of the battery pack;(5)The heating time of the heating film is short and the heating is uniform,while the hot air heating The heat pump can be used to achieve high-efficiency energy-saving effects,so the combination of these two heating methods can get the best heating effect.