Realizing Few-Layer Iodinene for High-Rate Sodium-Ion Batteries

Elemental 2D materials with fascinating characteristics are regarded as an influential portion of the 2D family. Iodine is as a typical monoelemental molecular crystal and exhibits great prospects of applications. To realize 2D iodine, not only is it required to separate the weak interlayer van der Waals interactions, but also to reserve the weak intramolecular halogen bonds; thus, 2D iodine is still unexploited until now. Herein, atomically thin iodine nanosheets (termed "iodinene") with the thickness around 1.0 nm and lateral sizes up to hundreds of nanometers are successfully fabricated by a liquid-phase exfoliation strategy. When used for the cathode of rechargeable sodium-ion batteries, the ultrathin iodinene exhibits superb rate properties with a high specific capacity of 109.5 mA h g^-1 at the high rate of 10 A g^-1 owing to its unique 2D ultrathin architecture with remarkably enhanced pseudocapacitive behavior. First-principles calculations reveal that the diffusion of sodium ions in few-layered iodinene changes from the original horizontal direction in bulk to the vertical with a small energy barrier of 0.07 eV because of the size effect. The successful preparation and intensive structural investigation of iodinene paves the way for the development of novel iodine-based science and technologies.