Cylindrical Cell Battery Packaging With Immersion Thermal Management: A Numerical Performance Study

Lithium-ion batteries are currently at the forefront of development due to higher incentives of automotive electrification and higher employment of renewable energies. This battery chemistry, and its derivatives, offer some of the highest energy densities among competing chemistries; however, adequate thermal management is required to operate safely and for an extended period of time. For this reason, thermal management systems and thermal analyses of battery cells and packs are of interest in the literature and industry, with novel proposals on packaging, control and materials being made. This paper proposes a partial direct thermal management solution for a 158.8 Wh battery pack consisting of nine 21700 cells and investigates its effectiveness in temperature homogeneity, maximum temperature reached within the pack and additional metrics such as the gravimetric energy density and cost. The analysis is performed numerically, in COMSOL, and is centered around the comparison between the proposed solution and the air-cooled and complete immersion variants. Two packaging assemblies are evaluated; the first, being used for natural and forced air convection cooling, sets the baseline, as well as used to evaluate partial immersion cooling at four varying levels: 25%, 50%, 75% and 100%. For each of these variations, two fluid flow rates are imposed. The second assembly aims to improve the thermal performance of the system, while maintaining low cost and mass. Each simulation is conducted under steady state conditions, with a 1C discharge rate.