Concurrent Hydrolysis Resistance and High Thermal Conductivity in Aluminum Nitride Enabled by Phase‐Engineered Graphene Encapsulation

Aluminum nitride (AlN) stands as a cornerstone material for next-generation thermal management, yet its notorious susceptibility to hydrolysis severely undermines long-term reliability. Here, we transcend conventional surface modification by introducing a phase-engineering strategy to fundamentally reconfigure the AlN surface. Through fluidized bed-chemical vapor deposition, we precisely construct conformal, high-crystalline and low-defective graphene "skin" on AlN powders (the intensity ratio of D-peak to G-peak ∼0.088), where the unique growth kinetics and interfacial phase are dictated by the AlN substrate, thus differ from the conventional non-metallic substrates. As revealed by density functional theory calculations, this process yields a covalently-bonded heterointerface characterized by distinct C-Al-N configurations, thereby moving beyond weak van der Waals interactions. The phase-engineered graphene skin delivers dual, synergistic functions, enhancing the thermal conductivity of AlN by 38.7% via optimized thermal transport pathways, while simultaneously acting as an ultrastable barrier, granting exceptional resistance to prolonged hygrothermal aging with the thermal conductivity variation of thermal interface material less than 1% in 30 days. This work resolves the long-standing trade-off between environmental stability and thermal performance in AlN, establishing a paradigm of phase-engineered graphene encapsulation for ceramic fillers, thereby enabling the scalable fabrication of robust, hydrolysis-resistant and high thermal conductivity composites.