Experimental Investigation of Temperature Homogeneity and Peak Temperature in a Battery Pack of Cylindrical Li-ion Cells Under Free and Forced Convection

Abstract

Electrical vehicles (EVs) are emerging as a suitable replacement for conventional IC engine-based automobiles because of their environmental friendliness. An EV is powered by a rechargeable battery pack usually made of Lithium-ion batteries and these batteries generate heat during their operation cycle due to exothermic reactions and ohmic effect. Thermal management of batteries is important for their safe operation and optimum lifespan. In this paper, a comparative analysis of temperature homogeneity, peak temperature and average temperature of battery pack is presented between free and forced convection-based Battery Thermal Management System (BTMS). Cells that are at higher temperature than average temperature of battery pack are more liable to fail earlier as compared to other cells of pack. Present research focuses on finding such critical cells in a battery pack consisting of twelve lithium-ion batteries. The battery pack is discharged at three different rates: 1C, 2C and 3C, and temperature of each cell is measured at regular intervals during the discharge process. The experimental results from present study revealed that free convection is better at maintaining temperature homogeneity, but peak temperatures were above 50 ̊C. Forced convection based BTMS was able to keep peak temperatures below 50˚C at 1C discharge rate but temperature homogeneity was not maintained within ideal limits of 5˚C. At higher discharge rates, the performance of both free convection and forced convection based BTMS is not within acceptable limits. Critical cells were identified to get better insight into limitations of conventional cooling systems so that better layout of battery module and better alternative methods of battery pack cooling can be developed.