Thermal model of cylindrical lithium-ion batteries

Due to their characteristic of providing high energy density and long cycle life, Li-ion batteries are being widely used as power sources for a range of applications, including electric vehicles. The temperature of a Li-ion cell is important for its performance, capacity, efficiency and safety, and it is strongly influenced by the charging and discharging process modalities. Especially during electric vehicle operation, considerable heat is generated in the battery pack that needs to be removed. In the present paper a simplified model for predicting the temperature trend within a battery module with cylindrical cells, is presented. This allows to estimate the requirements for a given cooling system under specific discharge conditions. Three cooling fluids have also been experimentally compared: air, a dielectric oil and a perfluorinated polyether. The best performance was shown by a commercial perfluorinated polyether, by which it was possible to work in safe conditions with a very low pumping power: at 0.02 W, a maximum temperature of 48°C is reached at the end of the discharge using Galden HT135, while 55°C is reached with the Midel ICE. The results also showed that, under the assumed conditions, an air-cooling system needs between 100 and 1700 times more energy than the other methods to keep the same average temperature.