Thermal Analysis And Optimization Of The Lithium-Ion Battery Pack For Pure Electric Vehicle

Lithium battery has gradually became the preferred battery of electric vehicle due to its advantages of high voltage,high energy density,long cycle life,low self discharge rate,less pollution and so on.Due to the limited space of the vehicle,lithium batteries are always closely arranged as battery package to provide power for the vehicle.Lithium battery will produce a lot of heat in charging and discharging process.If the heat is not dissipated in time,the temperature of battery package will rise continuously and the distribution of temperature will become heterogeneous,which may worsen the usability and safety performance of battery.In order to ensure the usability and safety performance of battery package,it is necessary to control working temperature and temperature difference of battery in normal range.In this paper,the CFD simulation technology was used to analyze the temperature distribution of lithium battery under different conditions and the temperature filed of lithium battery was simulated.Finally,the scheme was put forward to improve the temperature distribution of battery package.In this paper,the air cooling and liquid cooling of battery package were studied respectively.The main research works are as follows:(1)The 3D thermal effect model of lithium battery was constructed based on its heat generation and transfer mechanism,and the heat generation rate of lithium battery under different discharge rate was calculated.Through simulation,the temperature field distribution of lithium battery in different discharge rate and environment temperature was obtained.(2)The air cooling of lithium battery was simulated,and the effect of spoiler angle to battery cooling was investigated.It was found that the highest temperature and the maximum temperature difference can be both reduced and the battery temperature distribution can be improved through suitable spoiler angle design.Moreover,the effects of discharge rate,ventilation rate to the battery cooling were studied through simulation.It was found that the properly increasing of ventilation rate could lead to better temperature distribution of battery package.But a larger ventilation rate could lead to worse ability to improve battery package temperature distribution and even increasing of battery package temperature difference,which would cause the battery package temperature difference become worse.(3)The liquid cooling of lithium battery package was simulated,three different liquid cooling structures were designed and the effects of liquid cooling structure and coolant flow velocity to the cooling of battery package were analyzed.Result shows that compared to air cooling method,liquid cooling structure could more effectively reduce the temperature and control the temperature difference of battery package.As the battery was at 3C discharge rate and 0.005m/s coolant flow velocity,the highest temperature of battery package was controlled in normal working temperature range,but the temperature difference reached 18℃.Along with the increasing of coolant flow velocity,the highest temperature and temperature difference both decreased.As the battery was at 0.035m/s coolant flow velocity,the highest temperature and temperature difference of battery package were 32.6℃ and 5.7℃ respectively.(4)At last researched the pre heating performance at low temperature of the liquidcooling structure,found that this structure can pre heat the battery package at differen t temperature;and after 400s heating,the battery package reached 20℃,greatly improv ed the work condition of the lithium battery,expanded the application fields of the ele ctric vehicles.