Numerical investigation of fin geometries on the effectiveness of passive, phase-change material−based thermal management systems for lithium-ion batteries

Lithium-ion battery (LIB) packs serve as the primary energy storage solution for electric vehicles (EVs), but suffer from degraded performance under non-uniform and sub-optimal operating temperatures. Passive Thermal Management Systems (TMS) based on solid–liquid Phase Change Materials (PCMs) exhibit significant potential, however PCMs’ low thermal conductivity has limited their application. Integrating fins to improve heat transfer has been proposed, but there remains a lack of knowledge regarding how the system size and discharge time scale affects thermal performance with differing fin geometries. Here, a numerical model is developed using Ansys Fluent and validated to examine the time-resolved TMS performance with differing fin geometries under thermal loading and resting conditions. Two system scales are examined, with dimensions of the order of either 10 mm or 100 mm. For small-scale systems, fins offer no meaningful improvement compared to PCM alone: the best-performing fin geometry only reduces the maximum cell temperature by 0.2 °C at the end of a 720 s (5C) discharge. However, for the large-scale system, the performance depends strongly on the discharge duration. Of all geometries, 9 vertical fins are best performing at 480 s of discharge (38.3 °C maximum cell temperature with a 2.4 °C disuniformity), but become worst performing at 720 s (44.0 °C, 7.2 °C disuniformity). At 720 s, 7 horizontal fins instead become best performing (42.5 °C, 2.6 °C disuniformity) as large thermal gradients caused by convection are suppressed. Overall, we show via a Pareto analysis which geometries offer acceptable trade-offs between thermal performance and TMS mass.