| Lithium ion battery is widely used in the power storage and supply system of new energy electric vehicles.It has the advantages of good safety,long cycle life,high energy density and high working voltage.However,it,s safety and consistency in the high temperature environment are still very prominent,which limits the safety development of new energy electric vehicles.Therefore,the design of an effective battery thermal management system scheme is very important for the safety development of the new ener gy electric vehicle industry.Studies show that lithium ion battery is the mos t suitable working temperature range 25 to 50?,the system's maximum temperature difference should be controlled within 5 ?.Therefore,this paper studies the heat dissipation and average temperature of the ternary lithium cobalt oxide square battery by using phase change materials,and conducts in-depth research on the material modification and the heat dissipation design of the battery module.In this thesis,the heat generation mechanism of lithium cobalt oxide prismatic battery is studied.The research and development status of thermal management technology are analyzed and summarized,focusing on the thermal management technology based on composite phase change material(PCM).The properties of copper foam(CF)/expanded graphite(EG)/paraffin(PA)/epoxy resin(ER)composites were characterized.Subsequently,the corresponding CF/ EG/ PA/ ER composite phase change materials plates were designed.By comparing the PCM cooling with traditional air cooling via simulation and experiment e,the heat dissipation effect under different discharge rates and different air flow was analyzed.Furthermore,the thermal management strategy of composite phase change materials coupled with forced air cooling is applied to the battery module to investigate its feasibility for practical application.The main research contents of this paper are as follows:1.PA is used as the phase change substrate,EG is used as the PA containing skeleton,ER is used as the finalizing material,and CF is used as the heat conductive skeleton to prepare PA/EG/ER/CF composite plates.Through mechanical performance test,leakage performance test,thermal conductivity test,etc.,the result shows that the thermal conductivity coefficient of the composite phase-change material plate(CPCM-CF/EG)reaches 2.94 W/ m?K and the tensile and bending strength increases gradually after the introduction of CF.The results of mechanical properties test showed that in terms of bending strength,CPCM-EG/CF specimens were 3.6 times and 2.6 times better than CPCM-bald and CPCM-EG respectively.ER and EG significantly reduce leakage of PA and enhance the stability and safety of composite PCM plate.2.CPCM-bald,CPCM-EG and CPCM-EG /CF were applied to the lithium cobalt oxide battery module,and the heat dissipation effects are compared through experiments.In 5 C discharge rate,the highest temperature of CPCM-bald,CPCM-EG and CPCM-EG/CF battery module is 59.7?,57.7? and 54.7?,respectively.The CPCM-EG/CF battery module coupling with forced air convection with an air flow rate of 4 m/s shows dramatically cycling performance,i.e.,no heat accumulation phenomenon is observed during the cycling tests.The highest temperature and temperature difference of the battery module are controlled below 48?and 3.8?,respectively.3.The heat generation mechanism of the battery was analyzed,and the heat generation rate of the lithium cobalt oxide battery at 1,3,5 C discharge rate was calculated by combining theory and experiment.Fluent software was used to set the material qualitative,heat yield and boundary conditions of the single battery.The simulated data were compared with the experimental data of the third chapter analysis,finding that the temperature difference of the battery between experimental value and analog value in 1,3 and 5 C discharge rate are within 3?,which indicates the feasibility of single cell thermal model.Subsequently,a thermal model of phase-change materials was created.The CPCM-EG/CF battery modules were compared and analyzed by experiment and simulation at 5 C discharge rate with wind speed of 0 m/s,1 m/s,2 m/s and 3 m/s.The temperature difference between simulation and experiment is less than 3?,indicating multiple phase change materials thermal model is successful established.Based on the thermal model of the battery module of multielement with composite phase-change material composite board,the air duct was optimized to determine the location of the air inlet and outlet.With the wind speed of 3 m/s and 5 C discharge,the difference temperature of the battery pack reduce from 5.1?(design one)to 3.3 ?(design four).In addition,a preheating scheme in low temperature environment strategy for the CPCM-EG /CF battery module was designed based on the thermal model of the battery module of multielement phase-change material composite board.The result determines the power and heating time of the heating element are 40 W and 930 s,respectively. |
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