Enhanced Sodium-Ion Battery Performance by Structural Phase Transition from Two-Dimensional Hexagonal-SnS₂ to Orthorhombic-SnS

TLDR

Structural phase transitions can alter material properties without adding elements, offering significant technological value. The study reports a novel SnS@graphene architecture composed of two‑dimensional SnS and graphene nanosheets for use as a sodium‑ion battery anode. The SnS@graphene composite forms via a two‑step structural transformation (orthorhombic‑SnS → cubic‑Sn → orthorhombic‑Na₃.₇₅Sn) and exhibits synergistic Na‑storage reactions, while SnS₂ undergoes a three‑step transformation (hexagonal‑SnS₂ → tetragonal‑Sn → orthorhombic‑Na₃.₇₅Sn) during sodiation, as revealed by ex‑situ FTIR, XPS, and XRD. The annealed orthorhombic‑SnS shows superior sodium‑ion storage compared to SnS₂, and the SnS@graphene hybrid delivers a high specific capacity of 940 mAh g⁻¹ with excellent rate capability and cycling stability, outperforming most reported Na‑ion anodes and demonstrating its suitability for high‑performance energy storage.

Abstract

Structural phase transitions can be used to alter the properties of a material without adding any additional elements and are therefore of significant technological value. It was found that the hexagonal-SnS2 phase can be transformed into the orthorhombic-SnS phase after an annealing step in an argon atmosphere, and the thus transformed SnS shows enhanced sodium-ion storage performance over that of the SnS2, which is attributed to its structural advantages. Here, we provide the first report on a SnS@graphene architecture for application as a sodium-ion battery anode, which is built from two-dimensional SnS and graphene nanosheets as complementary building blocks. The as-prepared SnS@graphene hybrid nanostructured composite delivers an excellent specific capacity of 940 mAh g–1and impressive rate capability of 492 and 308 mAh g–1 after 250 cycles at the current densities of 810 and 7290 mA g–1, respectively. The performance was found to be much better than those of most reported anode materials for Na-ion batteries. On the basis of combined ex situ Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and ex situ X-ray diffraction, the formation mechanism of SnS@graphene and the synergistic Na-storage reactions of SnS in the anode are discussed in detail. The SnS experienced a two-structural-phase transformation mechanism (orthorhombic-SnS to cubic-Sn to orthorhombic-Na3.75Sn), while the SnS2 experienced a three-structural-phase transformation mechanism (hexagonal-SnS2 to tetragonal-Sn to orthorhombic-Na3.75Sn) during the sodiation process. The lesser structural changes of SnS during the conversion are expected to lead to good structural stability and excellent cycling stability in its sodium-ion battery performance. These results demonstrate that the SnS@graphene architecture offers unique characteristics suitable for high-performance energy storage application.