Optimization Investigation On The Cooling Structure Of Lithium-ion Battery Packages In Electric Vehicles

As the environmental pollution and the energy shortage are becoming more and more serious,much more attention has been paid to the electric vehicles.Due to the advantages of low energy consumption and zero emissions of electric vehicles,this industry has been developing rapidly in recent years.The key component of an electric vehicle is the power batteries.Temperature has a significant impact on the performance of batteries.If the heat generated during the battery charging or discharging process fails to be taken away timely,it will result in a reduction of the battery charging and discharging performance,and an acceleration of battery aging.What is worse,thermal runaway and explosion may happen.Therefore,it is of vital importance to develop an efficient battery thermal management system,so as to guarantee that the batteries are able to output maximum power within a safe temperature range.This work investigated the heat generation,transfer,and dissipation of lithium-ion batteries by using experimental and numerical methods.Structure optimizations of the heat management by air cooling and by liquid cooling were investigated,with the targets of maximum temperature and minimum temperature difference.The main conclusions of this work are summarized as follows:1.The discharging curves,the Ohmic resistance,the Coulomb efficiency,and the temperature distribution of a single lithium-ion battery were experimentally investigated.Besides,the temperature rises during the charging and discharging procedures were presented.2.An air cooling system of the battery package was designed.The temperature rises at different discharging rates under the conditions of the natural convection and the forced air cooling were experimentally investigated.A coupling thermal-fluid field numerical model was established.By using the heat generation power of each battery as the volume heat resource,the temperature rise response under the working condition of the forced air cooling and the 2C discharging rate was analyzed.The effectiveness of the simulation method was validated by comparing the simulation results with corresponding experimental ones.Thereafter,a cooling heat structure with much improved heat dissipation performance was achieved by means of an orthogonal design method,where the maximum temperature and temperature difference of the battery package were used as the evaluation indexes,and the influences of the air inlet angle,air outlet angle and air flow channel between battery cells were considered.3.According to the mechanism of the liquid heat transfer,a cooling plate heat transfer device with micro cooling tubes was designed.The both sides of the plate were attached to the silicon plates,which could mimic the heating process of the battery pack.A thermal-fluid coupled model was established to analyze the dissipation effect of the cooling plate.A cooling plate structure with a better cooling effect was achieved by means of the orthogonal design method,where the minimization of the maximum temperature was set as the optimization goal.Furthermore,the cooling effect of the cooling plate was verified experimentally.Finally,a multi-objective optimization method that combined the orthogonal design method with the iterative algorithm was used to perform multi-objective optimization analyses,where the maximum temperature and the minimum mass of the cooling plate were set as the optimization goal.4.Based on the optimized structure mentioned above,a liquid cooling system was designed for the battery package.The 2C discharging experiment was carried out to obtain the temperature distributions at the top and bottom sides of each battery.Thermal-fluid simulations were performed,and the results agreed well with the experimental data.Finally,the influences of the inlet temperature of the cooling liquid,and the flow rate on the maximum temperature of the battery package were numerically investigated.In addition,the influence of the curvature diameter of the cooling tube on the maximum temperature and the pressure difference of the battery package was also simulated.In conclusion,the temperature rise of the power battery can be control effectively through the structure optimization of the heat management system,which is of vital importance for engineering applications.