Graphene-silver hybrid nanoparticle embedded phase change materials for enhanced thermal management of lithium-ion batteries

Effective thermal regulation of lithium-ion battery (LIB) modules requires phase change materials (PCMs) with enhanced heat transfer capability without compromising latent heat storage. In this study, graphene nanoplatelet-silver (GNP-Ag) hybrid nanoparticles (NPs) were synthesized and incorporated at a low loading (0.1 wt%) into a paraffin-based PCM and evaluated using 3.0 mm and 6.0 mm cavity test rigs simulating battery module configurations. Compared to the base PCM, the hybrid composite exhibited a 20.37% enhancement in thermal conductivity (0.325 <i>vs.</i> 0.270 W m^-1 K^-1). The complete melting time was reduced by 17.26% in the 3.0 mm cavity configuration, while the overall heat transfer rate increased by 12.60% and 15.50% in the 3.0 mm and 6.0 mm cavities, respectively, demonstrating improved performance under both conduction and convection dominated regimes. Further, the composite exhibited a maximum overall heat transfer coefficient of 448.8 W m^-2 K^-1 and a Nusselt number of 2.07, marking a transition from a conduction-dominated to a convection-enhanced regime during the phase transition. In particular, the energy storage capacity increased significantly, reaching 1775.93 J in the 6.0 mm cavity compared to 892.15 J for the base PCM. The composite maintained stable phase change behaviour with low Stefan numbers (0.026-0.047), demonstrating a favourable balance between latent and sensible heat storage. Importantly, a comprehensive uncertainty analysis, performed following ISO/IEC GUM and ASME PTC standards, confirmed that the observed enhancements were statistically significant and within acceptable experimental error limits, thereby validating the reliability of the reported thermal improvements. These enhancements were achieved at minimal NP loading, ensuring cost-effectiveness and scalability, and thereby establishing the developed GNP-Ag hybrid NP embedded PCM as a reliable and economically viable solution for advanced LIB thermal management systems.