Few-Layer Antimonene: Anisotropic Expansion and Reversible Crystalline-Phase Evolution Enable Large-Capacity and Long-Life Na-Ion Batteries

Two-dimensional (2D) antimonene is a promising anode material in sodium-ion batteries (SIBs) because of its high theoretical capacity of 660 mAh g–1 and enlarged surface active sites. However, its Na storage properties and sodiation/desodiation mechanism have not been fully explored. Herein, we propose the sodiation/desodiation reaction mechanism of 2D few-layer antimonene (FLA) based on results acquired by in situ synchrotron X-ray diffraction, ex situ selected-area electron diffraction, and theoretical simulations. Our study shows that the FLA undergoes anisotropic volume expansion along the a/b plane and exhibits reversible crystalline phase evolution (Sb ⇋ NaSb ⇋ Na3Sb) during cycling. Density-functional theory calculations demonstrate that the FLA has a small Na-ion diffusion barrier of 0.14 eV. The FLA delivers a larger capacity of 642 mAh g–1 at 0.1 C (1 C = 660 mA g–1) and a high rate capability of 429 mAh g–1 at 5 C and maintains a stable capacity of 620 mA g–1 at 0.5 C with 99.7% capacity retent...