Enhanced activity of highly conformal and layered tin sulfide (SnS _x) prepared by atomic layer deposition (ALD) on 3D metal scaffold towards high performance supercapacitor electrode

Abstract

Layered Sn-based chalcogenides and heterostructures are widely used in batteries and photocatalysis, but its utilizations in a supercapacitor is limited by its structural instability and low conductivity. Here, SnS _x thin films are directly and conformally deposited on a three-dimensional (3D) Ni-foam (NF) substrate by atomic layer deposition (ALD), using tetrakis(dimethylamino)tin [TDMASn, ((CH ₃) ₂N) ₄Sn] and H ₂S that serves as an electrode for supercapacitor without any additional treatment. Two kinds of ALD-SnS _x films grown at 160 °C and 180 °C are investigated systematically by X-ray diffractometry, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy (TEM). All of the characterization results indicate that the films deposited at 160 °C and 180 °C predominantly consist of hexagonal structured-SnS ₂ and orthorhombic-SnS phases, respectively. Moreover, the high-resolution TEM analyses (HRTEM) reveals the (001) oriented polycrystalline hexagonal-SnS ₂ layered structure for the films grown at 160 °C. The double layer capacitance with the composite electrode of SnS _x@NF grown at 160 °C is higher than that of SnS _x@NF at 180 °C, while pseudocapacitive Faradaic reactions are evident for both SnS _x@NF electrodes. The superior performance as an electrode is directly linked to the layered structure of SnS ₂. Further, the optimal thickness of ALD-SnS _x thin film is found to be 60 nm for the composite electrode of SnS _x@NF grown at 160 °C by controlling the number of ALD cycles. The optimized SnS _x@NF electrode delivers an areal capacitance of 805.5 mF/cm ² at a current density of 0.5 mA/cm ² and excellent cyclic stability over 5000 charge/discharge cycles.