Integration of Heterogeneous Interfaces and Multi‐Dimensional Encapsulation Structure in Fe₂N@CNTs Enabling Highly Efficient Thermal Management and Microwave Absorption

Abstract The opposing effects of interface effect on phonon heat conduction and microwave absorption hinder the integration of thermal conduction with microwave absorption. Reconciling this contradiction by rationally optimizing the material structure remains a challenge. Herein, Fe₂N@CNTs with heterogeneous interfaces and multi‐dimensional encapsulated structures are fabricated through in situ chemical vapor deposition (CVD) to realize excellent thermal conductivity and microwave absorption. When the mass fraction of active material is 40 wt.%, the thermal conductivity (λ_//) of Fe₂N@CNTs composite films is 6.69 W m⁻¹ K⁻¹. The minimum reflection loss (RL_min) is up to −54.55 dB at a thickness of 3.43 mm, and the effective absorption bandwidth (EAB) is 5.52 GHz at 1.82 mm. The well‐designed Fe₂N@CNTs is an ideal model for gaining insight into electron transportation and phonon multi‐dimensional heat transport. Heterogeneous interface improves the dielectric loss and facilitates microwave and phonon absorption and conversion. The multi‐dimensional encapsulation structure increases the electron transport path and phonon heat transport paths making axial and radial co‐transfer possible. The multi‐dimensional encapsulation structure demonstrates extremely high microwave absorption and thermal management capabilities, which open up new possibilities for multifunctional applications in host materials with internal hollows.