Multi‐Stage Anisotropic Cellulose‐Based Aerogels via “Foam‐Flake‐Fiber” Interweaving for Versatile Microwave Absorbers

Abstract Controllable ice crystallization allows casting of isotropic or anisotropic porous aerogels to tailor versatile electromagnetic wave (EMW) absorbers. In this paper, a multivariate assembly‐assisted bidirectional differ‐speed freezing technique is developed to prepare the sandwiched nitrogen‐doped carbon micro‐foam/MXene/cellulose nanofiber aerogel (NCMF/MXene/CNF Aerogel, NCMCA). The NCMF, MXene, and CNF are assembled by alternating “foam‐flake‐fiber” through attractive interactions, and then undergo directional alignment under bi‐directional cross‐squeezing of ice crystals, forming a multi‐stage anisotropic structure containing integrated periodic grid‐like surface and honeycomb‐like channels. The high porosity results in ultra‐light density (6.2 mg cm −3 ) and thermal insulation (Δ T max = 140 °C). Silane deposition gives NCMCA a large water contact angle (≈133.6°) for anti‐icing. Multi‐component filling and compressive strain synergistically regulate electron transport and charge polarization for photothermal conversion, piezoresistive sensing, and microwave absorption. In particular, compression‐driven dielectric coupling facilitates dynamic modulation of EMW absorption. In addition, NCMCA is capable of efficiently absorbing EMW under far‐field conditions, thereby minimizing the radar scattering cross section. This work provides a novel structural design route for composite aerogels to achieve versatility, as well as new insights into the microstructural regulation mechanism of EMW absorption.