Hierarchical CoNi@C microspheres assembled by high-content CoNi nanoparticles interpenetrated into amorphous carbon for high-performance electromagnetic wave absorption

• High CoNi content with abundant magnetic/dielectric heterostructures supported by amorphous carbon were successfully constructed. • The dispersed CoNi nanoparticles construct multiple magnetic coupling networks and enhance magnetic loss. • The optimized hierarchical CoNi@C microsphere exhibits a broadband absorption of 6.6 GHz with a thin thickness of 1.65 mm. High content with good dispersity of magnetic components plays a crucial role in tailoring the instinct electromagnetic parameters and optimizing the impedance matching for high-performance electromagnetic wave (EMW) absorption materials, but remains a bottleneck due to severe self-agglomeration of the magnetic component. Here, hierarchical CoNi@C microspheres with CoNi nanoparticles uniformly dispersed in the carbon matrix are successfully fabricated by in situ carbothermal reduction coupling confined growth strategy. The metal Co 2+ and Ni 2+ are converted into CoNi nanoparticles and catalyze amorphous carbon transformation to graphite carbon, which simultaneously confines CoNi growth and effectively inhibits agglomeration. By modulating carbothermal reduction temperatures, controllable microstructure, synergistic dielectric-magnetic attenuation, and optimized impedance matching can be achieved. The optimized hierarchical CoNi@C microspheres exhibit superior EMW absorption performance with an effective absorption bandwidth (EAB) of 6.6 GHz at only 1.65 mm thickness. Systematic investigation demonstrates that the abundant heterogeneous interfaces contribute to enhanced interface polarization, graphitic carbon boosts conductivity, and the excellent magnetic loss originating from high-density confined CoNi nanoparticles facilitates impedance matching while reducing the application thickness. This study points to the avenue for synthesizing thin-thickness dielectric-magnetic composites with high content and dispersity of magnetic nanoparticles and deepens the exploitation of the corresponding EMW loss mechanism.