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[Display omitted] • A composite paper was prepared by combining aramid nanofibers, boron nitride nanotubes, and polyethyleneimine. • Elaborating interfacial hydrogen bonds design can optimize the mechanical properties of composite paper. • The composite paper has high thermal conductivity and unique dielectric performance. Aramid paper is ubiquitous in advanced electronics and high-voltage equipment by virtue of their outstanding dielectric properties, mechanical reliability, and thermal stability. However, their limited thermal conductivity still fails to satisfy the stringent demands for heat dissipation in applications with high power and high energy density. Herein, we report a highly thermally conductive composite paper prepared by synergistically combining one-dimensional (1D) aramid nanofibers (ANFs), 1D edge-hydroxylated boron nitride nanotubes (BNNTs), and polyethyleneimine (PEI). The resultant composite paper exhibits high thermal conductivity (9.91 Wm−1K−1), low dielectric loss (<0.01), and ultrahigh electrical breakdown strength (∼334 kV/mm) with an exceptional heat resistance performance. Three-dimensional hydrogen bonding networks were constructed between the ANF framework, PEI, and BNNTs, endowing the composite paper with a superior tensile strength (up to 317 MPa) and Young's modulus (∼7.7 GPa), which are significantly higher than those of the commercial Nomex T410 paper. This research provides important insights into the design and fabrication of multifunctional insulating paper for application in modern integrated electronic and power systems. [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]