Research On Air Cooling System Of Lithium-ion Battery Pack In Electric Vehicles

It is significant strategically for the development of electric vehicles to solve the global energy shortage, climate change and environment pollution. Battery technology is one of the three biggest core technologies in electric vehicles. Lithium-ion batteries are employed in electric vehicles widely because of large energy density, high charging and discharging voltage, low self-discharging rate. The manufacturing errors and using errors of batteries may cause different heat generating rates between the battery cells, which may make the battery temperature over high or temperature difference over large. Also temperature problems may cause the charging-discharging rates and charging-discharging states vary greatly between battery cells in turn. It may cause the thermal runaway or explosion when seriously. So the battery thermal management system design is very important to improve battery security and reliability based on maximum temperature and temperature difference.Forced air cooling system has great application value in battery thermal management system because of simple structure, low cost and easy to be controlled. The air cooling effects of lithium-ion battery pack are investigated by adopted the combination method of experiment and CFD simulation analysis in this paper. Firstly the charging-discharging experiment platforms of battery cell and battery pack are established to study the voltage characteristic and temperature characteristic in different charging-discharging rates. Then the three-dimensional simulation models of air cooling structure are built to simulate battery air cooling effects at 2C discharging rate based on battery heat generating mechanism and experimental data. The battery surface temperature and temperature difference of simulation results coincide with experiment results well, which verify the reliability of CFD simulation analysis method. Thirdly air cooling structure is optimized by single-factor analysis method and orthogonal test method based on three design factors including air-inlet angle, air-outlet angle and layout of battery spacing. The optimal combination levels of factors are obtained from range analysis. The air cooling effects of optimal model is improved greatly compared with initial model. The significance tests of these three factors are investigated from variance analysis based on simulation error, which point out the next optimizing direction of air cooling structure. Finally a reciprocating air flow structure is put forward based on the optimal structure. The reciprocating air flow strategy is studied from two aspects including reciprocating cycle and time cycle gap. The temperature difference of each battery cell decreases markedly and the battery temperature uniformity is improved greatly.Through these above studies, optimized forced air cooling system can meet the lithium-ion battery heat dissipation requirement. And Research methods and research results have great engineering value.