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

Abstract

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.

Pressure Engineering for Extending Spectral Response Range and Enhancing Photoelectric Properties of Iodine

“…Similar to these binary iodides, iodine is also a 2D layered semiconductor, and atomically thin iodine nanosheets have been successfully fabricated via a liquid-phase exfoliation method. [15,16] It should be noted that iodine is a molecular system, and in these nanosheets the iodine molecules are connected in the layer plane by halogen bonds rather than covalent bonds, which makes it a point of fundamental interest for this particular emerging material. [16][17][18] According to the Shockley-Queisser limit, iodine is very suitable for applications that require photo-responsivity due to its near-ideal bandgap of 1.43 eV, which is worth to be expected for the outstanding photoelectric properties.…”

Liquid‐Phase Exfoliated Few‐Layer Iodine Nanosheets for High‐Rate Lithium‐Iodine Batteries

“…[5] However, low electrical conductivity of iodine leads to sluggish kinetics and poor rate capability. [6][7][8][9] Moreover, high solubility of iodine in aprotic electrolyte results in fast capacity deterioration, "shuttle effect" (the dissolved iodine diffuses to the surface of lithium metal anode and react with lithium) as well as low columbic efficiency. [10,11] To address these issues, great efforts have been made to understand and improve the performance of iodine cathode.…”

“…2D iodine nanosheets were used in sodium iodine batteries in a previous work. [8] As a continuation, we use few-layer iodine nanosheets (FLINs) to improve the rate capability of Li-iodine batteries.…”

“…The abundant iodine resources in the ocean and low prices provide a reliable guarantee for the potential large‐scale applications [5] . However, low electrical conductivity of iodine leads to sluggish kinetics and poor rate capability [6–9] . Moreover, high solubility of iodine in aprotic electrolyte results in fast capacity deterioration, “shuttle effect” (the dissolved iodine diffuses to the surface of lithium metal anode and react with lithium) as well as low columbic efficiency [10,11] …”

“…Iodine is an orthorhombic system with a=7.379 Å, b=4.734 Å and c=9.620 Å, and it is layered structure along the (100) plane, [32,33] meaning the possibility of exfoliating layered iodine to iodine nanosheets due to weak van der Waals force between inter layers. 2D iodine nanosheets were used in sodium iodine batteries in a previous work [8] . As a continuation, we use few‐layer iodine nanosheets (FLINs) to improve the rate capability of Li‐iodine batteries.…”