High Sodium‐Ion Battery Capacity in Sulfur‐Deficient Tin(II) Sulfide Thin Films with a Microrod Morphology

Sulfur‐deficient SnS thin films for sodium‐ion battery anode application are prepared using aerosol‐assisted chemical vapor deposition. Growth directly onto the metal foil current collector forms sulfur‐deficient SnS microrod structures via a vapor–liquid–solid growth mechanism, with 92 nm average SnS crystallite size and an 800 nm film thickness. The sulfur deficiency is demonstrated with energy‐dispersive X‐ray analysis, powder X‐ray diffraction, and X‐ray absorption near‐edge structure analyses. This sulfur‐deficient SnS material demonstrates a very high capacity in sodium half cells. The first reduction scan at a specific current of 150 mA g⁻¹ shows a capacity of 1084 mAh g⁻¹. At the 50th cycle the specific capacity is 638 mAh g⁻¹ for reduction and 593 mAh g⁻¹ for oxidation. This capacity is demonstrated for tin sulfide itself without the need for a nanostructured carbon support, unlike previous high capacity SnS anodes in the literature. Both the capacity and ex situ characterization experiments indicate a conversion reaction producing tin, followed by alloying with sodium during reduction, and that both of these processes are reversible during oxidation.