Thermal optimization of cylindrical lithium-ion hybrid thermal management system based on shape-stabilized phase change materials under realistic operating conditions

To design such a hybrid battery thermal management system (BTMS), it is crucial to establish a practical and realistic approach from the point of view of: i. simulated operating conditions, ii. assumed materials/compounds, iii. Fast-charging performance test. To avoid oversizing, this work considers the World Harmonized Light-duty Vehicle Test Procedure Class 3 (WLTP3) driving cycle, instead of constant charge/discharge rates. Power requirements of a medium-sized vehicle during this WLTP3 cycle have been used to estimate the heat generated by the proposed battery module (18650 NMC cylindrical cells, hexagonal arrangement). This allows the minimum mass required by the phase change materials (PCM) to maintain the battery module at a given temperature threshold to be determined. Once this PCM mass requirement was established, a comprehensive optimization of the key thermal properties that characterize PCMs was carried out, investigating carbon-based additives (CBAs) to improve the low thermal conductivity of PCMs. The results show that the proposed approach can sustain up to 10 consecutive WLTP3 driving profiles without the need for additional energy input. This approach passively minimizes energy consumption during operation and absorbs up to 27 % of the heat emitted by the cell during fast charging, reducing the liquid cooling power requirement.