CFD and Experimental Investigation of Graphite Heat Spreader Based Cooling for Li-Ion Batteries for Electric Vehicles and EVTOL (Electric Vertical Take-Off and Landing) Aircraft Applications

Abstract Over the past few years, owing to different critical features such as high energy densities, safety, cycle-life etc., Lithium-ion batteries have been used successfully as an energy storage system for automotive applications. In addition, due to recent increase in interests towards developing EVTOL (Electric Vertical Take-Off and Landing) aircrafts, demand for Li-Ion batteries capable of providing high power discharge and charge along with above mentioned features has increased. Thermal Management System (TMS) is a critical component of a Li-Ion battery system that enables sustained high-power peak performance, improves overall life-cycle, and reduces possibility of thermal runaway during regular vehicle operation. The current article studies two different cooling configurations for thermal management of a commercially available 9 A-h Nickel Manganese Cobalt (NMC) Lithium-ion pouch cell for high C-rate conditions. The two configurations are referred to as the Double-sided cooling and Hybrid cooling, which includes a novel approach utilizing graphite-based heat spreader. The thermal performance for both configurations are studied through experimental testing and CFD (computational fluid dynamics) modeling. During experimental analysis, the pouch cell was subjected to high C-rate discharges of 3C, 4C and 5C using an Arbin controller and thermal test bench including a cold plate, mass flow meter, and temperature sensors. The temperature response of the cell is measured using T-type thermocouples that are strategically installed on its surface using a thermal interface material. For the numerical analysis, time-accurate, conjugate heat transfer-based 3D CFD simulations are conducted on high spatial resolution grids with a commercially available finite-volume method based CFD software. Numerical simulations at the mentioned C-rates are then run to explore the overall temperature distribution on the cell body. Temperature estimates from the numerical model are compared to the test data for the most aggressive 5C discharge condition. Both experimental testing and numerical modeling show that the Hybrid cooling approach provides higher rate of heat transfer compared to Double-sided cooling, owing to high thermal conductivity of graphite. Average cell surface temperatures using Hybrid cooling are ∼3°C, 3.7°C and 4.3°C lower than Double-sided cooling for 3C, 4C and 5C discharge conditions, respectively. The maximum measured cell temperature at the end of the most aggressive 5C discharge is 6°C lower in the case of Hybrid cooling. The temperature gradients are also less aggressive thereby allowing for a more uniform temperature distribution within the cell. Additional results in terms of flow and temperature distributions are also provided for the cold plate present in the cooling setup.