The inherent trade-off between impedance matching and electromagnetic (EM) attenuation capability has long been a fundamental limitation in carbon-based materials, hindering further advances in their EM absorption performance. To overcome this challenge, we innovatively designed hollow double-shell Co/carbon microspheres with a gradient graphitization structure, where Co₃O₄ nanoparticles preanchored on melamine formaldehyde (MF) microspheres can induce the formation of graphitic inner shells during high-temperature pyrolysis; nevertheless, the outer carbon shells remain amorphous due to the lack of corelated species, ultimately resulting in gradient graphitization from the inside. This unique double-shell architecture combines the advantages of both gradient graphitization and a hollow structure, which are favorable for powerful EM attenuation and impedance matching at the same time. EM analyses revealed that the outer amorphous carbon shells not only play a key role in optimizing impedance matching but also create heterogeneous interfaces with the inner graphitic shells to enhance interfacial polarization. As a result, the as-prepared sample achieves a superior reflection loss (RL) of −62.9 dB, and its maximum effective absorption bandwidth (EAB_max) can be extended to 11.3 GHz through a rationally designed multilayer structure, significantly surpassing that of its nongradient counterparts. Computer simulation technology (CST) simulations further verify a remarkable radar cross-section (RCS) reduction of 22.3 dB·m². This work provides an effective strategy for reconciling the conflict between impedance matching and attenuation in carbon-based materials and demonstrates their great potential as lightweight and broadband EM wave absorbing materials (EWAMs) in the future.

Electromagnetic (EM) absorption is paving the way to overcome the challenges related to conventional shielding strategy against EM pollution through sustainable energy dissipation. As characteristic functional media that can interact with electric or magnetic field branch, EM wave absorption materials (EWAMs) have received extensive attention and realized considerable development in the past two decades, where carbon-based composites are always considered as promising candidates for high-performance EMAWs due to their synergetic loss mechanism as well as diversified composition and microstructure design. Recent progress indicates that there is more and more interest in the fabrication of carbon-based composites with unique core–shell configuration. On one hand, core–shell configuration usually ensures good chemical homogeneity of final products and provides some positive protections for the components with susceptibility to corrosion, on the other hand, it creates enough heterogeneous interfaces between different EM components, which may bring enhanced polarization effect and intensify the consumption of EM energy. In this review, we firstly introduce EM wave absorption theory, and then highlight the advances of core–shell engineering in carbon-based composites in terms of built-in carbon cores and built-out carbon shells. Moreover, we also show some special core–shell carbon-based composites, including carbon/carbon composites, assembled composites, and decorated composites. After analyzing EM absorption performance of some representative composites, we further propose some challenges and perspectives on the development of core–shell carbon-based composites.