Thermal characterization of lithium iron phosphate pouch cells using a spatially resolving isoperibolic calorimeter

Abstract Thermal characterization of lithium-ion batteries is essential for optimal battery designs and their safe operation. In the present study, an in-house-built spatially resolving isoperibolic calorimeter was used to characterize the thermal behavior of a large-format commercially available lithium iron phosphate (LFP) pouch cell during operation. This highly sensitive calorimeter was used to analyze the total and local heat flow rates generated or absorbed by the cell under various operating conditions. To ensure the reliability of the measurements obtained by the developed calorimeter, the reversible and irreversible heat releases determined by the calorimetric methods were validated against those obtained by the electrochemical methods. The results of this study show that the characteristic thermal peaks and dips in the total heat generation of the studied cell are associated with the stage changes during the intercalation and deintercalation of lithium into the host electrodes, which is consistent with previous studies. Furthermore, a comparison of the heat flow rates generated under different initial operating conditions shows that higher heat release is predicted at higher current rates and lower temperatures. Finally, the distribution and uniformity of the heat flow rate over the surface of both fresh and aged pouch cells were investigated. The results indicate that the aged cell exhibits a higher magnitude of total heat generation with greater local variations compared with the fresh cell.