Ageing comparison of passive battery thermal management systems: Air cooling and loop heat pipes

Flat plate Loop Heat Pipes (LHPs) have emerged as an attractive battery thermal management system (BTMS) as they allow long-distance heat transfer at no power cost due to their unique porous structure. Additionally, the flat contacting surface is suitable for end cooling in cylindrical cells due to the higher axial thermal conductivity of the jelly roll structure. Previous studies on LHP BTMS have mainly focused on the cooling performance of prismatic or pouch cells, without considering cell ageing. This study instead numerically investigates the cooling performance, the resulting current distribution, and the ageing of a 6S4P 18650 battery module equipped with LHPs BTMS, comparing the performance against a natural air convection BTMS. This study has taken various thicknesses of the heat collector plate (i.e. 0.5 mm, 1 mm, 2 mm and 3 mm) and the number of LHPs (i.e. 1 or 2) into consideration. The results indicate that utilising a single LHP in conjunction with a 2 mm thick heat collector plate emerges as the optimal configuration. This design achieves a maximum average temperature of 29.7 degrees C and a minimal temperature gradient of 0.02 degrees C under a 1C discharge condition. The proposed design also significantly enhances battery lifespan, reaching up to 310 cycles with a maximum ageing gradient of 0.005, compared to the 146 cycles and 0.04 ageing gradient observed for the module with natural air convection. This study presents the potential of LHP BTMS for future electric vehicles, demonstrating its superior effectiveness in enhancing battery performance and longevity.