Rechargeable lithium ion batteries (LIBs) have transformed portableelectronics and will play a crucial role in transportation like electric vehicles. For higher energy storage in LIBs, two issues should be addressed, that is, fundamental understanding of the chemistry taking place in LIBs and discovery of new materials. Here we design and fabricate two-dimensional (2D) WS 2 nanosheets with preferential orientation of [001] and perfect single crystalline structures. Being used as an anode for LIBs, the WS 2 -nanosheet electrode exhibits high specific capacity, good cycling performance and excellent rate capability. Considering the controversy in the lithium storage mechanism of WS 2 , ex-situ X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) analyses clearly verify that the recharge product (3.0 V vs. Li + /Li) of the WS 2 electrode after fully discharging to 0.01 V (vs. Li + /Li) tends to reverse to 4 As is known, nanomaterials have the genuine potential to make a significant impact on the performance of LIBs, as their reduced dimensions enable high intercalation/deintercalation rates. The physical and chemical properties of nanostructured materials depend crucially on their morphologies and sizes. Therefore, nanomaterials have been widely explored to improve the electrochemical performance of LIBs, including 0D quantum dots, 40 1D nanoribbons, 41 2D nanosheets, 39 and 3D nanomaterials. 42 Herein, we fabricate the [001] preferentially-oriented 2D WS 2 nanosheets with perfect single crystal structures. As the anode for LIBs, the WS 2 -nanosheet electrode achieves a stable reversible capacity of about 539.1 mA h g -1 after 60 cycles at a current density of 0.2 A g -1 and a high rate capability.Considering the controversy in the lithium storage mechanism of WS 2 , ex-situ XRD, Raman and XPS analyses verify that the recharge product (3.0 V vs. Li + /Li) of the WS 2 electrode after fully discharging to 0.01 V (vs. Li + /Li) tends to reverse to WS 2 .More importantly, the [001] preferentially-oriented 2D WS 2 nanosheets with perfect single crystal structures could have immense potentials in other fields, for example, photocatalysis and hydrogen evolution reactions. 25,43 Experimental section
Fabrication of preferentially-oriented 2D WS 2 nanosheetsThe [001] preferentially-oriented 2D WS 2 nanosheets were fabricated by calcination of metallic W and S powders. The mixture of W and S powders (purity: 99.9 wt. %) with the atomic ratio of 1:2.1 was sealed in a vacuum quartz tube, and Figure 2. (a, b) Low-magnification TEM images, (c) SAED pattern, and (d, e) HRTEM images of the WS 2 samples. (f) Schematic illustration of plane (002) of WS 2 .Inset of (d) shows the FFT pattern corresponding to the HRTEM image. (g) STEM image of the WS 2 nanosheets, and (h, i) NB-EDX spectra corresponding to the marked areas by square 1 and 2 in (g) respectively.
