Fabrication of hollow MgO granules via freeze granulation as a filler for lightweight thermal interface materials

With the improvement in the performance of electric vehicles (EVs), heat generation by the battery increases, potentially leading to a number of issues; thus, the thermal management of high-performance secondary batteries is crucial. Thermal interface materials (TIMs) are polymer composites constituting high-thermal-conductivity fillers homogeneously dispersed in a polymer matrix. The thermal conductivity of TIMs is strongly affected by the thermal properties, size, shape, and content of the filler. As the weight of an EV directly impacts its fuel efficiency, new fillers with high thermal conductivity, low density, and cost-effectiveness must be developed for next-generation EVs. In this study, freeze granulation was used to fabricate highly thermally conductive, lightweight hollow MgO granules for low-density TIMs. Hollow MgO granules were fabricated by dispersing polymethyl methacrylate (PMMA) microbeads in a Mg(OH)2 slurry, freeze-granulating the slurry, and removing PMMA through sintering to create hollow MgO spherical-shaped granules. The heating rate during PMMA removal, the PMMA microbead content, and the solid content of the Mg(OH)2 in the slurry were adjusted to fabricate ideal hollow spherical-shaped granules. A TIM made with spherical hollow MgO granules (average diameter of 15–20 µm) fabricated through freeze granulation showed approximately 1% lower density and about 9% higher thermal conductivity than a TIM with solid MgO granules.