Heat generation characteristics of LiFePO₄ pouch cells with passive thermal management

This article experimentally investigates the heat generation characteristics and the effectiveness of passive cooling of commercially available LiFePO₄ (7.25 mm × 160 mm × 227 mm, 19.5 Ah) cells using different cooling materials. The specific heat capacity and the entropy coefficient of the cell are experimentally measured. The heat generation rate of the cell at 1-4 C current rates are also determined using three different methods: (1) the heat absorption calculated from the temperature increase of cooling water; (2) the energy loss calculated from the difference between the operating voltage and open circuit voltage; and (3) the energy loss during a charge-discharge cycle calculated using the voltage difference between charging and discharging. Results show that the heat generation rate estimated from heat absorbed by the water can be underestimated by up to 47.8% because of the temperature gradient within the cell and on the surface. The effectiveness of different passive cooling materials is compared at discharge current rates of 1-3 C. The average increase of the cell surface temperature is 22.6, 17.1, 7.7, 7.2 and 6.4^◦C at 3 C (58.5 A) using air, aluminum foam, octadecane, water with aluminum foam and water, respectively.