Construction of Dual 3D Networks in Boron Nitride/Aramid Nanofiber Films Enables High Thermal Conductivity and Mechanical Performance.

The intrinsically low thermal conductivity of meta-aramid insulation paper used within new energy vehicle drive motors leads to severe heat accumulation, posing a significant threat to operational safety. However, simultaneously achieving high thermal conductivity, superior electrical insulation, and excellent mechanical properties in meta-aramid insulation paper remains a formidable "trade-off" challenge. Herein, this study proposes a functionally decoupled "dual 3D network" strategy. By specifically confining multiscale modified boron nitride within rigid and flexible dual-conformation aramid nanofiber networks, mutually intertwined, dense thermally conductive and load-transfer dual 3D networks are successfully constructed. Benefiting from this unique architecture, the resulting composite film achieves a significant enhancement in both in-plane (18.25 W/(m·K)) and through-plane (0.94 W/(m·K)) thermal conductivities, representing remarkable increases of 4811.5% and 392.4%, respectively. Simultaneously, it endows the film with an outstanding dielectric breakdown strength of 184.1 kV/mm and a robust tensile strength of 96.41 MPa. Under a stringent 150°C oil-immersed thermal aging test, the film also demonstrates exceptional aging resistance. Molecular dynamics (MD) simulations reveal that this strategy triggers dense interfacial hydrogen bonding and intense dipole electrostatic interactions at the molecular scale, which creates robust interfacial anchoring nodes and highly efficient thermal conductive pathways.