Experimental Study of Heat Generation Rate during Discharge of LiFePO4 Pouch Cells of Different Nominal Capacities and Thickness

High manufacturing cost and thermal stability of Li-ion battery cells are currently the two main deterrents to prolific demand for electric vehicles. A plausible solution to this issue is a modular/scalable battery thermal management system (TMS). A modular TMS can ensure thermal reliability for battery cells of different capacities and size without needing major structural revision besides facilitating mass-production. However, understanding the relationship of heat generation rates with cell capacity and thickness is essential for developing a scalable TMS. The present paper discusses results derived from an experimental investigation undertaken with this purpose. Heat generation rates for LiFePO4 pouch cells of different nominal capacities are measured at discharge rates of 0.33C, 1C and 3C in ambient temperatures ranging between -10 and 50 degrees C using a custom-designed calorimeter. It is observed that heat generation rates of the LiFePO4 pouch cells become independent of their nominal capacity and thickness if the ambient temperature is regulated at 35 degrees C. In ambient temperatures lower than 35 degrees C though, the thin battery cells are found to be generating heat at rates greater than those of thick battery cells and vice-versa at temperatures over 35 degrees C for all discharge rates.