Research On Lithium Battery Thermal Management Structure And Temperature Control Performance Based On Composite Phase Change Materials

In recent years,people pay more and more attention to the environment and energy issues.Traditional cars constantly consume fossil fuels and bring a lot of exhaust gas,and electric vehicle technology is developing rapidly at home and abroad,which is the main development direction of new energy vehicles.Lithium-ion battery is the most widely used power battery in electric vehicles.Compared with other kinds of batteries,lithium-ion battery is more friendly to the environment,high voltage and light weight,but the performance of lithium-ion battery is closely related to the working temperature,as people’s requirements for mileage and charging speed increase,the energy density of lithium-ion battery is getting larger and larger,too high working temperature directly affects the life of lithium-ion battery.The thermal management of lithium-ion batteries is an effective and necessary measure.This paper conducts theoretical,simulation and experimental research on the heat dissipation of lithium-ion batteries,and the main research contents are as follows:(1)A two-layer EG/PW composite phase change material temperature control structure was prepared using two different phase change temperatures of paraffin wax(PW,37 ℃ and 46 ℃)as the phase change material and expanded graphite(EG)as the adsorbent material,which has a "relay race" type double buffer temperature control process.The optimal ratio of the composite phase change material was obtained by the thermal conductivity test and the leakage rate at 80 °C.The composite phase change material was observed and analyzed by scanning electron microscope and the latent heat value of the composite phase change material was measured by DSC.The temperature-controlled structure of the bilayer composite phase change material was applied to lithium-ion batteries at different ambient temperatures for discharge experiments.Compared with the single-layer structure,the double-layer composite phase change material temperature control structure can better control the temperature of the battery,and the maximum temperature of the battery at 5 C discharge rate is42 ℃ and 51 ℃ at 25 ℃ and 37 ℃ ambient temperature,respectively.(2)Using a phase change temperature of PW(44 °C),EG/PW was prepared based on the secondary encapsulation with silicone rubber(SR)to further reduce the leakage rate and multilayer graphene to enhance the thermal conductivity,and the EG/PW/SR/graphene composite phase change material with better thermal stability was prepared.The encapsulation effect of silicone rubber was analyzed using scanning electron microscopy,the leakage rate was tested at 120 °C,the thermal stability of the EG/PW/SR/graphene composite phase change material was analyzed by TGA,and the temperature control effect was tested by applying to lithium-ion batteries for discharge experiments.Silicone rubber can strengthen the stability of the composite phase change material and reduce the leakage rate,and 1% mass ratio of multilayer graphene possesses the effect of improving the thermal conductivity.The battery can be controlled below 50 °C at 5 C discharge multiplier and 25 °C environment.(3)A heat dissipation structure based on the coupling of the composite phase change material and the liquid cooling plate was designed and optimized.The simulation tested the heat dissipation effect of using only the composite phase change material at different ambient temperatures and different discharge rates,reflecting the necessity and effectiveness of combining with liquid cooling under more extreme conditions,tested the temperature control and heat dissipation effect of using the coupling structure on the battery pack,and designed different liquid cooling plate structures.By comparing the effects through simulation calculations and optimizing the liquid flow rate and direction,and further reducing the temperature difference of the battery pack by adding fins,the maximum temperature and temperature difference of the battery pack can be controlled within 50 ℃ and 5 ℃ respectively in 40 ℃environment and 5 C discharge multiplier.