Characterization and analysis of the effect of pressure on the performance of a large format NMC/C lithium-ion battery

When lithium ions intercalate and de-intercalate in the active materials, the cell experiences volume change induced by expansion and contraction. In vehicle applications, it is necessary to minimize negative effects caused by the volume change, such as module expansion and cracking which could lead to a loss of coolant flow or electrical isolation. We experimentally study the effect of compressive pressure on the electric and thermal performance of a pouch-type battery cell using a newly developed multi-functional calorimeter. The results reveal that while the capacity minorly changes, heat generation rate (HGR) tends to decrease as pressure increases, especially at high C-rates, which is further analyzed by the pressure effect on the heat source parameters, such as entropy coefficient and internal resistance, through the Hybridized Time-Frequency Domain Analysis (HTFDA) and Electrochemical Impedance Spectroscopy (EIS). Additionally, the sensitivity analysis of the pressure over capacity (dPdQ) reveals that the pressure development is indicative of the volume expansion and contraction behaviors, which is quantified by the measurement of cell strain using a dynamically controlled press. Furthermore, the pressure effect on the HGR is analyzed using an electrochemical-thermal model. The resulting HGR simulations are in good agreement with the experimental results.