Enhanced activity of highly conformal and layered tin sulfide (SnSx) 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, ((CH₃)₂N)₄Sn] and H₂S 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-SnS₂ and orthorhombic-SnS phases, respectively. Moreover, the high-resolution TEM analyses (HRTEM) reveals the (001) oriented polycrystalline hexagonal-SnS₂ 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 SnS₂. 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/cm² at a current density of 0.5 mA/cm² and excellent cyclic stability over 5000 charge/discharge cycles.