Salt-templated graphene nanosheet foams filled in silicon rubber toward prominent EMI shielding effectiveness and high thermal conductivity

Lightweight and multifunctional polymer-based composites with prominent electromagnetic interference (EMI) shielding effectiveness (EMI SE) and heat conductance are in urgent demand for developing highly integrated electronic devices in the 5G/6G era. Herein, ultrathin graphene nanosheet-based foams with many micropores are prepared by a general salt-template guided freeze-drying-calcination route with PEG 20000 and NaCl as a carbon source and a template, respectively. Calcination temperature (T) and PEG 20000/NaCl mass ratio (λ) were employed to modulate the texture, defects, graphitization, EM parameters, EMI SE, and thermal conductivity of graphene foams. The graphene foams formed under T = 800 °C and λ = 0.530 exhibited the optimal EMI SE and thermal conductivity. The EMI SE is beyond 20 dB over C, S, and Ku wavebands with a low filling ratio of 7 wt%, exceeding most graphene-based materials. Meanwhile, three-dimensional (3D) interconnected frameworks reduce inter-nanosheet contact thermal resistance and provide continuous frameworks for thermal and electrical conduction, engendering a larger heat conductivity (3.26–3.95 W m−1 K−1) under a lower filling ratio (3–5 wt%) compared to most reported composites. Together with their high SBET (255.6–670.5 m2 g−1) and light weight, the graphene foams synthesized in this research are expected to be utilized as a thermally conductive and EMI shielding filler for advanced electronic packaging.