The Influence of Cell Temperature on the Entropic Coefficient of a Lithium Iron Phosphate (LFP) Pouch Cell

The reversible (entropic) heat source contributes to the thermal behavior of a lithium-ion battery in particular at the initial state of charge and discharge. One factor that affects the magnitude and direction of the reversible heat is called the entropic coefficient (EC). The objective of this research is to calculate the varying entropic coefficient values of the lithium-iron phosphate battery. A 14Ah lithium ion pouch cell, with a dimension of 220 mm × 130 mm × 7 mm, was studied in both charge and discharge. The SOC levels range from full charge to full discharge in 5% increments. The temperature levels vary from −20°C to 55°C in 5°C increments. It reveals that there is a strong influence of cell temperature on the entropic coefficient when the cell is at its extreme upper or lower SOC level. A correlation was obtained to relate the EC to temperature and the SOC by curve fitting the experimental data. Calorimetric data of the test cell was also presented that shows the influence reversible heating has on the overall rate of heat generation within the cell. The calorimetric data and the EC measurement were combined to determine the irreversible heat generated in the cell.