Thermal Management Of Power Battery Based On Flexible Phase Change Materials With High Thermal Conductivity

Phase change temperature control technology used in power battery thermal management system has the advantages of simple structure,no power components,good temperature control effect and so on.Paraffin phase change materials have the advantages of high latent heat,high specific heat,low undercooling,good electrical insulation,light weight and no corrosion,which are suitable for thermal management of power batteries.Low thermal conductivity and easy leakage during solid-liquid phase transition are two significant disadvantages of paraffin as phase change temperature control materials.The results show that the phase change temperature control component is hard,poor deformation coordination,not easy to fit closely with the surface of the battery,resulting in obvious interface thermal resistance.In this paper,paraffin wax is used as the core phase change material to develop a flexible composite phase change material with high thermal conductivity.(1)Based on the analysis of heat generation mechanism and calculation of heat generation rate of single Li Fe PO₄battery with rated voltage of 3.2V,the material composition of high thermal conductivity flexible composite phase change material was determined,that is,40 industrial paraffin was used as phase change material,SEBS as elastic carrier,graphene as high thermal conductivity additive.A series of flexible composite phase change materials with high thermal conductivity were prepared by melt blending method.Through the test and analysis of the macro setting effect,microstructure characteristics,phase transformation characteristics,thermal conductivity and contact thermal resistance of the samples,it is determined that the better formula is paraffin:SEBS:graphene equal to 15:4:1.The latent heat of phase change is about 90.74J/g,and the thermal conductivity is 30%higher than that of pure paraffin.(2)By analyzing the heat generation mechanism of the battery and establishing the thermal simulation model of the battery,the thermal management of the battery is carried out under different physical parameters of phase change materials(thermal conductivity,phase change temperature point,phase change latent heat),arrangement of phase change materials(single-layer or double-layer phase change material structure)and different contact thermal resistance The phase change temperature of the phase change material determines the final temperature of the battery surface.Generally,the phase change temperature of the phase change material is 3?5?higher than the ambient temperature.When the thermal conductivity of the phase change material is higher than the thermal conductivity of the battery,then increase the thermal conductivity of the phase change material,the thermal management effect is not obvious.The greater the contact thermal resistance is,the worse the thermal management effect is When the contact thermal resistance is larger than 3.86×10^-2(m~2?K)/W,PCM will lose its thermal management effect,and the surface temperature of the battery is almost the same as that without PCM.(3)Through the experimental study of simulated battery cooling system,the influence of different cooling methods on the thermal management effect of battery was explored.The results show that the cooling effect is the best when the liquid cooling plate is in direct contact with the surface of the battery,and the final temperature of the battery surface is maintained at about 26?after working for one hour at 6.6W heating power.Compared with the natural air cooling without cooling method,the time required for the battery surface to reach the dangerous temperature of 50?is increased by 69%and 115%respectively by using D-PCM and D-PCM+Liquid cooled plate cooling methods,and the time_DT_-PCMand T_{D-PCM(10)liquid cooled plate}for the battery to keep in the optimal working temperature range are increased by 43%;When using method S-PCM,the cooling effect is further improved,the time required for the surface of the battery to reach the dangerous temperature of 50?is increased by 208%,and the time_ST_-PCMfor the battery to keep in the best working temperature range is increased by 171%.The combination of PCM and liquid cooling plate can effectively reduce energy consumption S-PCM+liquid cooling plate W5S5.The energy consumption of S-PCM+liquid cooling plate W5S10 method is 50%and 66.67%respectively,and the final surface temperature is36.493?and 37.164?respectively.