Efficient thermal management of electronic devices by constructing interlayer phonon bridges.

Layered film-based thermal management materials with high in-plane thermal conductivity can effectively diffuse point heat sources and prevent local overheating. However, their low through-plane thermal conductivity limits its overall heat dissipation. Here, we introduce a honeycomb-gel densification strategy that forms zigzag yet continuous interlayer phonon bridges within the layered structure. This design establishes bi-directional thermal pathways, boosting both in-plane and through-plane thermal conductivity by 488.9% and 503.3% of the aramid nanofiber/boron nitride nanosheet, respectively, compared to random-gel densified films. Also, the aramid nanofiber/boron nitride nanosheet film exhibits high solar reflectivity, infrared emissivity, and thermal radiation, enabling efficient subambient cooling (17.2 °C at 100 mW/cm²) for heat-generating devices.