Research On The Temperature Field Of A Soft Pack Lithium Battery And The Realization Of Its Thermal Management System

Energy shortage and environmental pollution are two major world problems that need to be solved urgently.Electric vehicles use power batteries as energy sources,which greatly reduce the consumption of fossil fuels.The energy density of the battery is very high,and a lot of heat will be released in the process of use.If the heat generation cannot be dissipated in time,the power battery temperature will be too high and affect the normal use safety and service life of the battery.Therefore,how to reduce the battery temperature rise and improve the homogenization of power battery has become the focus of power battery research.In this paper,the heat generation and heat dissipation of a soft-pack lithium ion battery for an electric vehicle are studied.The main research contents are as follows:(1)After consulting relevant literatures at home and abroad,the analysis shows that the internal heat production of ternary lithium battery can be divided into reaction heat,ohmic heat and polarization heat,which are respectively related to the temperature rise coefficient of the battery electromotive force,ohmic internal resistance and polarization internal resistance.A mathematical model for thermogenesis of softencapsulated lithium ion battery is established.(2)The performance test platform of lithium ion battery was set up to conduct charge and discharge test,discharge temperature rise test,internal resistance test and electromotive force temperature rise coefficient test.The temperature rise curves of the battery surface under different ambient temperatures and discharge rates were obtained.The variation curves of ohmic resistance and polarization resistance of lithium battery with SOC(State Of Charge)at different discharge rates and ambient temperatures;The variation trend of temperature rise coefficient of electromotive force of lithium battery with SOC.(3)A three-dimensional simulation model of flexible package ternary lithium battery monomer is established.The effects of ambient temperature and discharge rate on surface temperature rise were studied.The simulation results are compared with the experimental data measured in the battery temperature rise experiment,which verifies that the battery heat generation model established in this paper can accurately reflect the internal heat generation of the battery with high accuracy.(4)In this paper,the battery pack is cooled by liquid cooling plate liquid,the working medium of which is 50% glycol.The influence of fin width,outlet height,number of channels and fin length on the heat transfer performance of liquid cooling plate was studied.According to the orthogonal test method,a four-factor four-level experiment scheme was established to study the joint effects of the number of flow channels,the length of fins,the width of fins and the height of the outlet on the performance of the liquid-cooled plate.JF factor,a comprehensive performance parameter,was used as the evaluation standard to obtain the structure of the liquidcooled plate with the best performance.(5)A heat dissipation model composed of 15 single lithium batteries and the liquid cooling board with the best performance was built by CATIA,and the heat dissipation performance of the battery group was analyzed by transient simulation.The influence of inlet temperature,flow rate and ambient temperature of coolant on the heat dissipation performance of the liquid cooling plate was studied.The heat dissipation performance of the battery is improved by replacing the insulating silica gel between the batteries with aluminum sheets and by replacing the vertical placement of the battery pack with horizontal placement.