Novel passive thermal management of batteries at cell level: introducing air pocket to PCM jacket of a battery

The performance and efficiency of electric vehicles (EVs) heavily depend on Lithium-ion batteries (LIBs). However, their overheating can lead to reduced battery life, safety concerns and compromised EV performance. As such, to ensure battery safety and durability while maintaining optimal performance, thermal management of LIBs at cell level is imperative. More so, the demand for longer driving ranges and faster charging times, critically necessitates the management of the thermal behaviour of LIBs. Accordingly, as active cooling technologies in EVs impose complexity and consume energy, passive cooling alternatives has interestingly emerged. Therefore, the present study evaluates the fundamental impact of introducing air pockets into a Phase Change Material (PCM)-based passive cooling jacket for battery cells. Consequently, different air pocket thicknesses (0.5 mm, 1.1 mm, 1.4 mm and 1.7 mm) were tested within the PCM jacket (with conserved and non-conserved PCM volumes). The investigation focused on a commercial LIB cell (Panasonic 18,650 PF) and assessed temperature, voltage, and state-of-charge for EV applications. The results showed that introducing a 1.4 mm air pocket into a conserved-volume PCM achieved optimal passive thermal management. Indeed, the proposed thickness reduced the pure PCM jacket's thermal conductivity by 0.5 % and improved the liquid fraction's longevity by 40%. These practical thermal management improvements had minimal impact on system volume and weight in the proposed passive design. In the non-conserved PCM volumes, where minimizing the battery thermal management system (BTMS) weight was prioritized, a 0.5 mm air pocket apparently surfaced as the optimal solution, enhancing thermal performance with a variance of 5 %. Also, the analysis through temperature contours disapproved the effectiveness of a 1.7 mm air pocket in a non-conserved PCM volume. It emphasized the promising results associated with a 0.5 mm air pocket at 3000 s, highlighting its optimal performance in extending thermal capabilities while considering system constraints.