Copper-triggered phase reconstruction synergizes with sulfur vacancy-engineered for impedance-matching optimization

The proliferation of modern electronic devices has led to increasingly severe electromagnetic interference (EMI), posing risks to both information security and human health. Transition metal sulfides (TMSs) are promising candidates for electromagnetic (EM) wave absorption owing to their tunable crystal structures, strong dielectric polarization, and chemical stability. However, the coexistence of multiple phases and complex defect dynamics makes it challenging to precisely tailor their EM parameters, resulting in limited absorption efficiency and bandwidth. Herein, we propose a copper-triggered phase reconstruction strategy integrated with sulfur-vacancy regulation to achieve synergistic dielectric-magnetic optimization. Cu-doped CoS_1.035/Co₃S₄@C nanosheet heterostructures were synthesized via a hydrothermal-annealing route. The cooperative tuning of phase and defect states effectively decouples dielectric loss and magnetic attenuation, leading to superior impedance matching and enhanced EM energy dissipation. The optimized composite achieves a minimum reflection loss of -60.8 dB at 1.86 mm and a broad effective absorption bandwidth of 5.76 GHz at 1.7 mm, with a low filler loading of only 20 wt.%. This study establishes a phase-defect coupling paradigm for designing lightweight, broadband, and high-efficiency sulfide-based EM absorbers, providing new insights into the microstructure-property relationship of conductive polar materials. This study establishes a phase-defect coupling paradigm for designing lightweight, broadband, and high-efficiency sulfide-based EM absorbers, providing new insights into the microstructure-property relationship of conductive polar materials.