All‐Dielectric Ultra‐Broadband Microwave Absorbing Aerogel with Optimized Dielectric Dispersion via Dielectric Relaxation Time Regulation

The limited conceptual understanding and lack of effective techniques for optimizing dielectric dispersion continue to hinder the development of all-dielectric broadband microwave-absorbing materials (MAMs) with minimal thickness. In this study, a strong theoretical correlation between dielectric relaxation time and dielectric dispersion behavior is established by applying the ideal dielectric dispersion law in conjunction with Debye theory. This led to a strategic approach aimed at extending the relaxation time to optimize dielectric dispersion and achieve broadband microwave absorption without incorporating magnetic components. To realize this, fluorinated graphene (FG) is engineered to stack with MXene nanosheets, resulting in the fabrication of MXene/fluorinated graphene/cellulose nanofibers (MXene/FG/CNFs) aerogels. This configuration significantly extended the dielectric relaxation time of interfacial dipoles from 9.2 ps in MXene/CNFs to 19.5 ps in MXene/FG/CNFs aerogels, corresponding to a fluorine content of 35% in FG. This extension is attributed to increased interfacial dipole moments from strong electronic delocalization induced by highly electronegatively fluorine atoms. The improved structure yield progressively optimized dielectric dispersion, resulting in a maximum effective absorption bandwidth (EAB_max) of 9.08 GHz at a thickness of 2.54 mm and a low density of 34.4 mg cm^-3. Moreover, the hybrid aerogel also exhibited fascinating Joule heating, thermal insulation, and compressive strength.