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Dielectric materials with superb thermal and electrical properties are highly desired for high-voltage electrical equipment and advanced electronics. Here, we propose a novel strategy to improve the performance of epoxy composites by employing boron nitride nanosheets (BNNSs) and γ-glycidyl ether oxypropyl sesimoxane (G-POSS) as functional fillers. The resultant ternary epoxy composites exhibit high electrical resistivity (1.63 × 1013 Ω·cm) and low dielectric loss (<0.01) due to the ultra-low dielectric constants of cage-structure of G-POSS. In addition, a high thermal conductivity of 0.3969 W·m−1·K−1 is achieved for the epoxy composites, which is 114.66% higher than that of pure epoxy resin. This can be attributed to the high aspect ratio and excellent thermally conductive characteristics of BNNSs, promoting phonon propagation in the composites. Moreover, the epoxy composite simultaneously possesses remarkable dynamic mechanical properties and thermal stability. It is believed that this work provides a universal strategy for designing and fabricating multifunctional composites using a combination of different functional fillers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hybrid particles are synthesized from boron nitride and barium titanate. • Composite films prepared by incorporating hybrid particles into cyanoethyl cellulose. • The composite exhibits a high dielectric constant of ∼ 44. • High thermal conductivity and breakdown strength are also achieved in the composite. Polymer dielectrics hold a great potential to be used in the field of power equipment and advanced electronics. However, their limited thermal conductivity fails to satisfy the imperative demand for heat dissipation in practical applications. Herein, we report a novel strategy to prepare multifunctional cyanoethyl cellulose matrix composite films by employing a hybrid filler of boron nitride nanosheets and barium titanate nanoparticles. The resultant composite films simultaneously exhibit high thermal conductivity (∼10.54 W/m·K), high dielectric constant (∼44), high electrical breakdown strength (>302 kV/mm), and low dielectric loss (∼0.01). The findings in this work enable broader application of polymer dielectrics in impulse power and energy storage devices. [ABSTRACT FROM AUTHOR]