Analytical modeling and optimization of phase change thermal management of a Li-ion battery pack

Highlights: • Carries out iterative heat transfer analysis of phase change cooling of Li-ion cells. • Identifies key design trade-off between discharge rate and energy storage density. • Compares the performance of phase change cooling with convective cooling. • Contributes towards safe and efficient energy storage through effective cooling. -- Abstract: Thermal management of Li-ion cells is critical for safety and performance of energy conversion and storage in battery packs in a variety of applications. Phase change cooling is a promising approach towards this goal. In contrast with several recent papers on experimental measurements of this approach, there is a distinct lack of literature in theoretical modeling of phase change cooling of Li-ion cells. This paper presents a theoretical model for solving the coupled heat transfer problem involving the cooling of a heat-generating Li-ion cell with a phase change material. Results show that while phase change cooling effectively reduces cell surface temperature, the cell core continues to remain quite hot. Improvement in cell thermal conductivity is shown to be critical for fully benefiting from phase change cooling. On the other hand, the impact of increasing thermal conductivity of the phase change material plateaus out at large values. Trade-offs between thermal management and energy storage density of a Li-ion battery pack are analyzed by quantifying the extent of temperature rise and reduction in energy storage density at large discharge rates. Comparison of phase change cooling with convective cooling is also presented, indicating key trade-offs in these approaches. These results contribute towards understanding the fundamentals of phase change cooling of Li-ion cells, as well as improving the performance of practical thermal management systems for Li-ion cells.