Scalable Production of Highly Conductive 2D NbSe₂ Monolayers with Superior Electromagnetic Interference Shielding Performance

Thin, flexible, and electrically conductive films are in demand for electromagnetic interference (EMI) shielding. Two-dimensional NbSe₂ monolayers have an electrical conductivity comparable to those of metals (10⁶-10⁷ S m^-1) but are challenging for high-quality and scalable production. Here, we show that electrochemical exfoliation of flake NbSe₂ powder produces monolayers on a large scale (tens of grams), at a high yield (>75%, monolayer), and with a large average lateral size (>20 μm). The as-exfoliated NbSe₂ monolayer flakes are easily dispersed in diverse organic solvents and solution-processed into various macroscopic structures (e.g., free-standing films, coatings, patterns, etc.). Thermal annealing of the free-standing NbSe₂ films reduces the interlayer distance of restacked NbSe₂ from 1.18 to 0.65 nm and consequently enhances the electrical conductivity to 1.16 × 10⁶ S m^-1, which is superior to those of MXenes and reduced graphene oxide. The optimized NbSe₂ film shows an EMI shielding effectiveness (SE) of 65 dB at a thickness of 5 μm (>110 dB for a 48-μm-thick film), among the highest in materials of similar thicknesses. Moreover, a laminate of two layers of the NbSe₂ film (2 μm thick) with an insulating interlayer shows a high SE of 85 dB, surpassing that of the 20-μm-thick NbSe₂ film (83 dB). A two-layer theoretical model is proposed, and it agrees with the experimental EMI SE of the laminated NbSe₂ films. The ability to produce NbSe₂ monolayers on a tens of grams scale will enable their diverse applications beyond EMI shielding.