Environmentally Stable and Highly Crystalline MXenes for Multispectral Electromagnetic Shielding up to Millimeter Waves

Abstract Advanced electronics and telecommunication devices rely on electromagnetic (EM) waves of a wide frequency range during their operation, thereby necessitating the development of efficient and ultrathin materials for electromagnetic interference (EMI) shielding across multispectral EM waves, particularly those exceeding 100 GHz, equivalent to millimeter wavelengths. Here, this study reveals that highly crystalline Ti 3 C 2 T x MXene exhibits excellent EMI shielding performance across a multispectral frequency range from 100 kHz to 110 GHz, along with outstanding environmental stability and processability for solution coating and film fabrication. Notably, the highly crystalline Ti 3 C 2 T x MXene films exhibit the highest electrical conductivity (18,000 S cm −1 ) and remarkable environmental stability (maintaining >95% electrical conductivity over one year), coupled with effective EMI shielding (up to 106 dB at 110 GHz with an ultrathin thickness of 10 µm), surpassing five other MXenes, including Nb 2 CT x , V 2 CT x , conv.‐Ti 3 C 2 T x , Ti 3 CNT x , and Mo 2 Ti 2 C 3 T x , and different synthetic materials. Furthermore, increasing the thickness, electrical conductivity, and frequency enhances the shielding performance. These results demonstrate the potential of applying MXenes to next‐generation portable electronics, radar systems, and autonomous vehicles. This study also provides insight into the fundamental shielding mechanisms related to material thickness, electrical conductivity, and frequency of EM waves.