Research On Thermal Management System Of Power Battery Based On Composite Phase Change Materials

The safety and reliability of the power battery is one of the important factors to ensure the safe driving of electric vehicles,and the lithium-ion battery in the power battery is greatly affected by temperature,and the normal use of the battery will be affected under high temperature and low temperature,resulting in Battery capacity decay,shortened cycle life,and thermal runaway of the battery.Therefore,it is of great significance to study how to control the operating temperature of lithium-ion batteries and make them work within a safe temperature range.In this paper,combined with the existing instruments and equipment in the laboratory and the ongoing National Natural Science Foundation of China project,the composite phase change material(CPCM)with high latent heat,high thermal conductivity and low leakage rate was prepared through experiments,and a set of CPCM and water-jacket liquid-cooling coupled temperature control structure model was designed.The heat dissipation and temperature control performance of square and cylindrical lithium-ion batteries were studied to ensure their safety.The main research contents and conclusions of this paper are as follows:1.Using paraffin wax(PW)as temperature control material,expanded graphite(EG)and graphene as adsorption and thermal conductivity enhancement materials,and combining with metal aluminum honeycomb to further improve its thermal conductivity and structural strength,the experimental preparation of high latent heat,high thermal conductivity PW/EG/graphene/aluminum honeycomb CPCM,applying it to square lithium-ion batteries.Through analysis and characterization,performance testing and verification experiments,the results show that:(1)The addition of graphene can effectively improve the thermal conductivity of PW.(2)eeping the content of EG unchanged,when the content of graphene added is 2 %,the thermal conductivity of PW/EG/graphene/aluminum honeycomb CPCM is 7.125 W/m·K,compared with PW without graphene added The thermal conductivity of /EG is only 3.809 W/m·K,and its thermal conductivity is increased by 87.06 %.(3)Under the discharge rate of 1 C and1.5 C,CPCM was used in the temperature control research of square lithium-ion battery,and it was found that it could control the temperature rise rate and the maximum surface temperature of the battery and maintain it within the suitable temperature range of45 ℃,which ensures the safe operation of the battery.2.The PW is encapsulated with heat-resistant silicone rubber(SR)to reduce its leakage rate.At the same time,combined with EG and aluminum nitride(AlN)powder to synergistically enhance thermal conductivity,a morphologically stable PW/EG/AlN/SR CPCM was prepared,which was applied to cylindrical lithium-ion batteries.Through analysis and characterization,performance testing and verification experiments,the results show that:(1)Controlling the mass fraction of EG,the thermal conductivity of PW/EG/AlN/SR CPCM will increase continuously with the increase of AlN mass fraction.(2)When the mass fraction of AlN is 9 %,its thermal conductivity is 0.735 W/m·K,the latent heat value of phase transition is 62 J/g,and the leakage rate is 7.26 % after heating in a constant temperature box at 150 ℃ for 10 h.(3)The application of PW/EG/AlN/SR CPCM to cylindrical lithium-ion batteries can control the maximum temperature of the battery surface within the safe range of 50 ℃ under the battery discharge rate of 1.5 C and 2 C,which shows that the prepared CPCM can ensure the safe operation of the cylindrical lithium-ion battery under a certain discharge rate.3.Aiming at the heat dissipation problem of cylindrical lithium-ion battery packs,a heat dissipation and temperature control structure with PW/EG CPCM coupled with water jacket liquid cooling is designed.Through the simulation analysis,the results show that:(1)CPCM can better absorb the heat generated by the battery pack,increase the distance between the batteries,and gradually reduce the maximum surface temperature.(2)The use of the coupling structure can further reduce the maximum surface temperature of the battery pack,and with the increase of the number of liquid cooling channels,the maximum surface temperature of the battery pack also gradually decreases.(3)The 6-channel water jacket type liquid cooling-CPCM heat dissipation and temperature control structure has the best temperature control effect.At the end of the discharge rate of 3 C and 5 C,the maximum surface temperature of the battery pack was 33.78 and 41.11 ℃,respectively,which were reduced by 1.68 and 0.62 ℃,respectively,compared with the 3-channel structure.(4)The maximum temperature difference of the battery pack increases gradually with the increase of the discharge rate,but it can be controlled within a safe temperature range of 5 ℃,which can ensure the safe operation of the battery pack and help improve its cycle use.