Thermal Management Of Automotive Lithium Iron Phosphate Batteries Based On The Coupling Of Phase Change Materials And Liquid Cooling

The square lithium iron phosphate battery with low cost,long cycle life,good thermal stability,and high safety performance is widely used in pure electric vehicles.But the battery in the charging and discharging process will generate a lot of heat due to electrochemical reactions.Too poor heat dissipation may lead to internal short circuit,thermal runaway and other problems.In addition,the temperature difference between the battery monomer is too large,which will also affect the performance and life of the battery.Therefore,effective thermal management of the battery is essential.This thesis outlines the classification and characteristics of pure electric vehicle power batteries,the current status of research on battery thermal management,and focuses on the current status and characteristics of thermal management technologies coupled with liquid cooling and other methods.For the thermal management design of single battery,the coupling heat dissipation structure of the battery module is proposed on this basis,and its effectiveness is verified under the cycle condition of the whole vehicle.The specific research content and research results are as follows.Firstly,the structure and working principle of a lithium-ion battery are introduced,the heat production principle and heat transfer characteristics of a lithium-ion battery are analyzed.The heat production model of square lithium iron phosphate battery is established and validated.The passive thermal management of a single-cell battery based on composite phase change material(PCM)and the active thermal management system coupled with phase change material and liquid cooling are proposed for singlecell battery.The effect of the PCM bonding method,cooling tube type and flow direction on the heat dissipation effect of the single cell was also investigated by numerical simulation in the FLUENT software.The results show that the use of phase change materials on one or both sides of the battery will result in a sudden increase of the maximum temperature difference in the late stage of discharge.The use of U-shaped tubes is better than straight tubes,and changing the coolant import and export directions has little effect on the reduction of the maximum temperature.These set the scene for later studies.Then,between the use of phase change materials alone does not meet the heat dissipation needs of the battery,liquid cooling heat dissipation has the advantages of high heat transfer,high specific heat capacity,and better cooling performance,etc.On the basis of the active thermal management system of single-cell battery,a liquid cooling structure of the battery module based on phase change materials is proposed.The cooling flow channel does not directly contact with the battery,which avoids the cold volume and concentration,and can solve the difficult heat dissipation of the battery along the height direction of the battery.The phase change temperature of phase change material is selected as 32℃,and the open valve temperature is selected as 40℃,which is the result of the comprehensive consideration of making full use of the latent heat of phase change material and reducing the open valve ratio.Finally,according to the technical parameters and performance indexes of the vehicle,the drive motor and power battery pack are selected and designed.A model of the dynamics of a pure electric vehicle was constructed using AMESim 1D modelling and simulation software.The model dynamic performance is verified and the current distribution characteristics of the battery pack under typical working conditions are obtained.The results show that the maximum temperature and maximum temperature difference of the battery module are within the temperature range allowed for the optimal operation,verifying the effectiveness of the designed cooling system.This thesis has 67 pictures,13 tables,and 130 references.