Enhanced hydrophobicity of MgO as a Thermal Management Filler for Battery

As the markets for electric vehicles (EVs) and energy storage systems (ESS) continue to grow, the importance of effective battery thermal management has become increasingly critical. Therefore, there is a growing demand for thermal interface materials (TIMs) with highly thermal conductivity. Magnesia (MgO) is an attractive lightweight thermal management filler, yet its rapid hydration and poor compatibility with hydrophobic polymers limit practical use in various applications including battery pack system. Here, we investigated two different silane-based surface-engineering strategies, direct fluorinated alkylsilane grafting (denoted as F-MgO) and a tetraethyl orthosilicate (TEOS)-assisted hybrid coating followed by FAS treatment (TF-MgO), to identify the key design parameters governing hydrophobic stability and composite-level dispersion. Experimental results reveal that F-MgO highly exposed fluorocarbon layer with CF₃ and CF₂-CF₂ groups, whereas TF-MgO contains a silica-rich interphase that partially embeds or reorients fluorinated chains. As a result, F-MgO exhibits the highest water contact angle (128.27 °) and markedly suppressed moisture uptake under 85 °C/85% RH aging. 2D X-ray Micro CT imaging and Raman mapping of PDMS composites further demonstrate that F-MgO achieves void-free and homogeneous filler dispersion, while pristine MgO and TF-MgO particles show aggregation-induced microstructural defects. This study establishes that maximizing surface exposure and packing density of fluorocarbon functionalities is essential for producing hydrophobic, moisture-resistant, and uniformly dispersed MgO fillers, offering a practical pathway to high-reliability thermal management materials for next-generation battery applications.