| Lithium-ion batteriy are widely used in the power battery pack of new energy vehicles because of its excellent performance.During the driving or charging and discharging process of new energy vehicles,the lithium-ion battery will release a lot of heat,and the temperature of the battery pack will rise.If the part of the heat cannot be discharged in time and the battery pack temperature is higner than the maximum temperature allowed by the battery,there is a risk of burning whick will endanger the safety of the occupants.At the same time,when the vehicles is in a low temperature,the graphite embedding capacity in the battery electrode decreases,and the battery performance cannot be fully used.If a hign current charging is performed,thermal runaway or even a safety accident may occur.Therefore.The thermal runaway management of the lithium-ion battery pack that research its cooling scheme at high temperature and preheating scheme at low temperature have extremely important theoretical and practical value.The thermal runaway cooling scheme and preheating scheme designed in this thesis mainly focus on the following technical issues for in-depth research and discussion:(1)Analyze the current research results of domestic and foreign research scholars on the comparison of cooling schemes,the factors affecting the cooling effect and selection of preheating schemes,and determine the main methods and key technologies used in this study.Compare the advantages and disadvantages of several common car batteries,choose the prismatic lithium-iron phosphate battery studied in this article.Studythe working principle,heat generation principle and thermal characteristics of the prismatic lithium-iron phosphate battery to determine the best operating temperature range.(2)In this thesis,on the basis of the traditional liquid-cooling bottom plate,two vertical cooling plates are added.The maximum temperature and temperature distribution of the battery pack using this cooling model structure can be well controlled.Besides,the same cooling model structure can be used to preheat the battery pack under low temperature,with simple control and no-additional cost features.(3)Carry out the battery cooling scheme design,aiming at the high discharge rate that air-cooling cannot provide effective cooling results,design a liquid-cooling scheme,analyze and study its performance under different conditions.Use Star ccm+simulation software analyzes the cooling performance of each cooling scheme,it was found thatthe cooling performance of scheme using 2 vertical cooling plates(both containing 4 cooling channels)and 1 cooling bottom plate(including 2 cooling channels)is the best.Then conduct response surface optimization design for the scheme,when the diameter of the cooling pipe is 7.5 mm,the coolant temperature is 10.888℃ and the thermal conductivity of the material is 4.956 W/(m·K),the temperature balance is the highest with a value of 97.512%.(4)In response to the problem that the battery pack needs to be preheated before it can be used normally under low temperature,a preheating scheme is designed to study the role of the scheme in different preheating liquids and temperatures.On the basis,the preheating strategy is improved,and compare the preheating effect of the scheme under different liquid entry and exit sequences.The solution thatthe liquid with a certain temperature flow first and then take the battery pack discharge has the best preheating performance.Besides,when the U-shaped pipes are used as the preheating pipes in the vertical plates,the preheating performance will be improved.Then conduct response surface optimization design for the scheme,when the diameter of the preheating pipe is 8.054 mm,the preheating liquid temperature is 32.394℃ and the thermal conductivity of the material is 4.976 W/(m·K),the temperature balance is the highest with a value of 96.061%. |
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