Aramid nanofiber (ANF) paper has shown potential applications in flexible electronics. However, its inherent low thermal conductivity coefficient (λ) values might threaten the safety of devices under a high-power working condition. In this work, polydopamine-functionalized boron nitride nanosheet (BNNS@PDA)/ANF thermally conductive composite papers with nacre-mimetic layered structures were prepared via highly efficient vacuum-assisted filtration followed by hot pressing. For a given BNNS loading, the surface functionalization of BNNS could further enhance the thermal conductivities and mechanical properties of BNNS@PDA/ANF composite papers. BNNS@PDA/ANF composite papers presented anisotropic thermal conductivities, and the through-plane (λ⊥) and in-plane (λ∥) values of the 50 wt % BNNS@PDA/ANF composite papers reached 0.62 and 3.94 W/mK, 181.8 and 196.2% higher than those of original ANF paper, respectively, which were also higher than those of 50 wt % BNNS/ANF composite papers (λ⊥ = 0.52 W/mK and λ∥ = 3.33 W/mK). The tensile strength of the 50 wt % BNNS@PDA/ANF composite papers reached 36.8 MPa, 30.5% higher than that of 50 wt % BNNS/ANF composite papers (28.2 MPa). In addition, the heat resistance index (T HRI) of the 50 wt % BNNS@PDA/ANF composite papers was further increased to 223.1 °C. Overall, our fabricated BNNS@PDA/ANF composite papers possess highly thermal conductivities, excellent mechanical robustness and flexibility, and outstanding thermal stabilities, showing great potential applications in the fields of intelligent wearable equipment, flexible supercapacitors, and flexible electronics.

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