Asymmetric conductive polymer composite foam for absorption dominated ultra-efficient electromagnetic interference shielding with extremely low reflection characteristics

Absorption-dominated electromagnetic interference (EMI) shielding polymer composites with low reflection are greatly desired for next-generation electronic devices due to their minimization of secondary electromagnetic radiation pollution. However, realizing highly efficient EMI shielding with microwave absorption-dominated features remains a great challenge. Herein, a flexible, extremely low reflection and ultraefficient EMI shielding waterborne polyurethane (WPU) composite foam with a unique asymmetric conductive network and oriented porous structure is assembled through a special density-induced filler separation combined with a directional freeze-drying method. The asymmetric conductive network is constructed from the highly conductive Ag-coated expanded polymer bead (EBAg) particles aggregated on the top of the foam as a conductive layer and the low conductivity graphene-supported iron-cobalt (FeCo@rGO) magnetic nanoparticles deposited at the bottom as an impedance matching layer. Because of the asymmetric network with rational layout of the impedance matching layer and conductive shielding layer, the composite foam exhibits an outstanding EMI SE of nearly 90 dB (84.8 dB on average) in the X band. The average reflection efficiency is only 0.3 dB, and the reflectivity is as low as 0.08, which is the lowest value for EMI shielding materials ever reported. Furthermore, benefitting from this asymmetric filler network structure, the composite foam exhibits excellent compression recovery and satisfactory water-resistant shielding stability. Our work provides a new strategy for designing ultraefficient EMI shielding materials with reliable absorption-dominated features and is highly promising for applications in next-generation electronic devices.