| Lithium-ion battery has been widely used in the electric car,because of its high voltage,high energy density,good cycle,no memory effect,no pollution,etc.The lithium ion battery will produce a lot of heat in the process of charge and discharge,the heat is not timely or not at that time,the battery will cause local temperature is too high,the temperature distribution is not uniform,seriously affect the battery capacity and rate performance,service life,stability,and even lead to accidents.So,the temperature field of the lithium-ion battery thermal management of battery,the highest temperature control,and as far as possible to maintain consistency between the battery temperature of each battery,to ensure the battery safe working temperature range.In this paper,the finite element analysis,simulation and experimental research methods are applied to simulate and test the temperature field of lithium ion batteries with different configurations during charging and discharging at different rates.On this basis,the design and optimization of the heat dissipation scheme of the battery pack are discussed.The main research contents are as follows:Firstly,the heat generation principle and heat transfer mechanism of Li ion battery during charging and discharging are studied.The differential equations of heat conduction and the thermal model of cylindrical coordinate system for cylindrical battery are established.Second,the temperature field test of single cell 18650 Li ion battery was carried out to study the temperature change of different position of Li ion battery under different charging and discharging rate.The results show that the temperature of the middle part of the monomer battery is the highest,and the temperature at the positive end is slightly higher than the negative end.The temperature of each point at different positions of single cell increases with the discharge rate,and the temperature difference in different positions of the battery increases.On the other hand,ANSYS was used to simulate the temperature field of the single lithium ion battery.The simulation results were consistent with the experimental results.The simulated temperature and the experimental temperature error of the battery were less than 3%..The rationality of the battery simulation model and thermal parameters of the battery were proved.Third,according to the composition and requirements of the battery pack,100 batteries are connected in parallel to form a battery module,and the arrangement of the battery is designed in three different ways:side by side,staggered and stacked.The temperature distributions of three kinds of batteries under different discharge rates were analyzed by using ANSYS software.The simulation results show that the temperature rise of the battery is the lowest,and the temperature difference between the batteries is the smallest.The simulation results show that the battery arrangement is better by side-by-side arrangement.Fourth,in order to improve the local temperature of batteries at high discharge rate in the process of high temperature and uneven distribution,the paper adopts serial parallel ventilation and side by side ventilation to cool the battery.Fluent software was used to simulate the temperature rise of the battery in different ventilation rates and the temperature difference between the batteries in each part of the battery under two different ventilation modes.The simulation results show that the temperature rise of the parallel ventilation battery is lower and the temperature distribution is more uniform.Finally,the influence of different wind speed,different cold air inlet temperature and different heat dissipation medium on the temperature field characteristics of the battery is analyzed by using Fluent software.At low discharge current,by increasing the air flow rate to temperature rise and the temperature distribution uniformity effectively improve the battery,the battery to meet the cooling demand;at high magnification(5C)discharge current,improve the air velocity and reduce the inlet air temperature of the battery pack can also meet the battery safety needs.On the other hand,the simulation results show that the use of liquid medium cooling can also effectively ensure that the battery works in a safe temperature range during the high rate discharge. |
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