| In order to overcome the energy crisis and environmental pollution caused by traditional vehicles,new energy vehicles are needed to replace traditional vehicles.Power battery is the main energy source of new energy vehicles and the most important link.In addition to the high energy density,high cruising range and long cycle life,the power battery needs to be fully guaranteed.Although the power battery is one of the three major sources of new energy,it is very sensitive to temperature,and generates a lot of heat during the work process.If it is not cooled in time,the reliability and service life of the battery will be greatly reduced.Therefore,an efficient thermal management system is needed to ensure efficient and stable operation of the battery.In order to improve the performance and safety of the battery,a high thermal conductivity composite phase change material was prepared and applied to battery thermal management.The main research contents are as follows:The composite phase change materials with carbon fiber and multi-walled carbon nanotubes as thermal conductive additives were prepared respectively.The composite phase change materials with different mass fraction of carbon additives and different carbon fiber and multi-walled carbon nanotubes were studied,and their appearance and osmosis were observed.Leakage rate,thermal conductivity,and the impact on battery thermal management were investigated.Research indicates:?1?There is no chemical reaction between the composite phase change materials prepared by melt blending,but simply combined physically.?2?The thermal conductivity of the composite phase change material increases with the increase of the content of CF and WMCNTs.When the content of CF and WMCNTs is 6wt%and9wt%,respectively,the thermal conductivity is 4.78Wm-1K-1,which is 3.06 of PW/EG.Times.?3?The leakage rate of the composite phase change material decreases with the increase of CF and WMCNTs.When the content of CF and WMCNTs is 6wt%and 9wt%,respectively,the leak rate is 1.12%,which is 0.169times of PW/EG.The paraffin wax is used as the phase change material by the melt blending method,the high density polyethylene is used as the support material,the expanded graphite and the carbon fiber are the heat conductive additives,and the composite phase change material of the aluminum honeycomb plate with the spur structure is added by 3D printing.After the phase change material undergoes multiple solid-liquid phase transformation processes,the mechanical strength will be greatly reduced.Therefore,this chapter introduces 3D printing aluminum honeycomb with spur structure to improve its mechanical strength and compare it with the performance of ordinary aluminum honeycomb.The microstructure,thermal properties,thermal conductivity,stress strain and thermal response of the surface of the composite phase change materials were investigated.The results show:?1?When the CF mass fraction is 4.5%,the degree of undercooling is reduced by 51.5%and 43.3%,respectively,compared to PW PCM and PW/EG CPCM.?2?When the CF mass fraction is 4.5%,the thermal conductivity of the PW/EG/CF/HDPE composite phase change material increases to 5.723 Wm-1K-1,which is 1.9 times that of PW/EG.?3?At a uniform pressure of 100 KPa,the strain is only 1.25 mm.?4?The composite phase change material also has excellent battery thermal management performance,and the battery surface temperature is controlled within a safe temperature range of 50°C or less at a discharge rate of 2.5 C.This paper uses a square aluminum shell ternary lithium battery provided by Jiangxi Xingying Technology Co.,Ltd.to establish a three-dimensional thermal model of a single cell by analyzing the thermal characteristics of the lithium battery and obtaining physical parameters such as thermal conductivity,density and specific heat capacity of the battery.The ANSYS Fluent software was used to simulate the charging and discharging process of the battery,and the temperature change cloud during the discharge of the battery was obtained.The simulation results are compared with the experimental results.The results show that the simulation results of the three-dimensional thermal model of the battery established by ANSYS Fluent software have a high similarity with the actual heat generation behavior of the battery.Finally,a 3D printed aluminum honeycomb with a spur structure was surface-coppered and then fabricated into a composite phase change material plate using the same method and applied to battery thermal management.The battery was subjected to a cyclic charge and discharge test to record changes in the surface temperature of the battery.Compared with the simulation results of ANSYS Fluent software,the results show that the thermal conductivity of the composite phase change material plate increases to 6.23 Wm-1K-1 after copper plating on the surface of the 3D printed aluminum honeycomb,and its thermal management effect on the battery is better. |
PDF Full Text Request