Thermal characterization of 18650 lithium iron phosphate cell for wide ranges of temperature and discharge rate to identify most efficient operating window

Abstract

Accurate measurement of heat generation and thermal characterization of lithium-ion batteries is crucial for the design and development of efficient battery thermal management systems. In the present study, an isothermal battery calorimeter is employed for precise and reliable measurement of heat generation rate. Thermal characterization of 18650 cylindrical lithium iron phosphate (LFP) cell is conducted across a wide range of discharge rates (0.5C–6C) and operating temperatures (10 °C–60 °C). It is observed that discharge capacity decreases with increasing C-rate and decreasing temperature. The decline is more pronounced at higher discharge currents and for temperatures below 20 °C. Moreover, cell capacity remains stable at higher temperatures (30 °C–60 °C). It is also observed that the Heat Generation Rate (HGR) significantly increases at lower temperatures and higher C-rates, with the maximum HGR doubling as the temperature drops from 60 °C to 10 °C at 0.5C. The same is 19-fold when the discharge rate increases from 0.5C to 6C at 60 °C. A counterintuitive endothermic trend is observed at low discharge rates (0.5C–1C) and high temperatures (40 °C–60 °C). Heat is absorbed instead of released. It indicates the role of the entropic heat coefficient. Finally, from these trends, what came out of the characterization exercise is the preferred window of cell operating conditions, in terms of temperature and discharge rate. These are identified on the basis of the cell discharge efficiency (CDE) map for the chosen 18650 LFP cell.