Identifying pressure drop and heat transfer correlations for a liquid-cooled lithium-ion battery pack model of electric vehicles under hot-cold driving

The performance of a full lithium-ion battery (LIB) pack with its cooling system depends on the pressure drop and heat transfer from the cell to ambient air through coolant, cooling flow channels, air gaps, and pack cases. Predicting the LIB pack responses (i.e: voltage, SOC, temperature) requires accurate predictions of the thermal performance between the cells and ambient air and cooling flow behaviour inside the pack, respectively, since the pack has several thousand cells, cooling channels, and channel pipe bends. This work presents a systematic approach to identifying heat transfer and pressure drop ∆P correlations that capture the real-time thermal-electrical performance of a mass-produced LIB pack under constant speed (in winter) and transient driving (in summer). A vehicle test is conducted using a Tesla Model Y, a long-range, dual-motor model equipped with a 75-kWh LIB pack. The LIB pack's thermal and electrical performance is recorded under both constant speed and transient driving conditions. The electrochemical NCA/Gr-SiOx Li-ion cell is developed and validated using experimental data before being reduced to an equivalent circuit model, which accelerates pack-level simulation with a complete cooling circuit model. An approach to identifying pressure drop and heat transfer correlations is discussed, with pack model validations conducted at coolant temperatures ranging from 0 to 40 °C and coolant flow rates of 4 to 14 L/min. Thermal and electrical performances (voltage, SOC, ∆P, and temperatures of the coolant, brick-to-brick, and module-to-module) of the high-fidelity battery pack model are validated against vehicle test data at 60 km/h driving (ambient temperature Ta = -10 °C) and repeated FTP+HWFET cycle (Ta = 30°C). This work can be used as a guideline to design BTMS using model-based development.