Electrochemical-thermal modeling and experimental validation of commercial graphite/LiFePO 4 pouch lithium-ion batteries

Large-sized lithium-ion battery (LIB) mathematical models are critical in design of cells, packs, and their associated thermal management systems. A high-fidelity fully coupled electrochemical-thermal model for a commercial 20 Ah LIB is developed to simulate the distribution of electrochemical and thermal variables three-dimensionally (3D) through 48 electrode layers in the pouch cell. As a new feature, the details of heat generation and voltage drop due to the tab, current collectors, and associated contact resistances are included in the developed model. A series of galvanostatic charge/discharge tests at operating rates ranging from 1C (20 A) to 5C (100 A) and at room temperature is conducted on the pouch cell and the output voltage and temperature distribution are recorded. The developed model voltage and temperature distribution predictions are successfully compared against the experimental data, demonstrating the accuracy of the model. As a key finding in this work, it is found that self-heating is the main contributor for electrochemical performance improvement in large-sized LIBs over small cells. This is due to the improved kinetic and transport properties of LIB electrodes at elevated temperatures. It is also demonstrated that the temperature variation between the surface and center layers of a pouch cell is not significant at a maximum difference of about 1.7 °C for charge/discharge rates up to 5C (100 A). As a result of this finding, it is suggested that a single temperature measurement close to the tabs at the battery surface would be sufficient for thermal management development and control purposes.