Experimental study on the influence of temperature and state-of-charge on the thermophysical properties of an LFP pouch cell

Past research has shown that the specific heat capacity and thermal conductivity may be influenced by the battery's temperature and/or its state-of-charge (SOC). However, there has not been any clear relationship uncovered between these test parameters and the thermophysical properties of the battery. Therefore the objective of this research is to measure the thermophysical properties of a Lithium Iron Phosphate (LFP) pouch cell at different surface temperatures and SOC levels. An isothermal calorimeter is used to measure the specific heat capacity at various temperature points and SOC levels. This same instrument is then reconfigured to perform as a heat flow meter apparatus and yield cross-plane thermal conductivity measurements. A commercially available 14 A h pouch cell was used as the test specimen. On average, the specific heat capacity of the cell increases slightly with temperature but remains independent of SOC. The behavior of the cross-plane thermal conductivity is opposite in nature. Its value increases with decreasing SOC but is largely unaffected by temperature. A lithium-ion battery with electrolyte has nearly twice the thermal conductivity of the dry cell version without electrolyte.