Scalable Synthesis of Few-Layered 2D Tungsten Diselenide (2H-WSe2) Nanosheets Directly Grown on Tungsten (W) Foil Using Ambient-Pressure Chemical Vapor Deposition for Reversible Li-Ion Storage

Abstract

Abstract Body: Sustainable energy storage devices demand new materials for energy storage systems, which alleviate their cost and increase longevity. A prominent energy storage technology for modern applications is Lithium-ion batteries. In this regard, two-dimensional (2D) materials attracted substantial and considerable attention due to their unique properties and abundant potential in various applications, including batteries1. Controllable synthesis of 2D materials with high quality and better efficiency is essential for their large scale applications, such as their functions as electrode material in batteries. The methods for the synthesis of two-dimensional materials include exfoliation, solvothermal, and chemical vapor deposition (CVD) routes, among which CVD offers better quality, efficiency, and consistency. In this perspective, the family of 2D transition metal di-chalcogenides (TMDCs) gained significant attention for their ability to store metal ions such as Li, Na, and Mg. TMDCs of group 6 transition metals (MX2 where M = Mo, W, and X = S, Se, Te) have a lamellar structure (space group P63/mmc) similar to graphite but with larger interlayer spacing. Tungsten di-chalcogenides are significant here because of the larger size of W that provides a further alteration of the 2D structure and has been successfully utilized for various applications such as photodetectors, field-effect transistors (FETs), etc. The typical group 6 TMDC lattice structure show W atoms confined in a trigonal prismatic coordination sphere neighbored to Se atoms. Because of its very high density (~9.32 g cm−3), WSe2 also has a high volumetric capacity, thereby proving it as a prospective LiB electrode material2. Our work focuses on a facile synthesis of 2H-WSe2 on W foil in the ambient-pressure chemical vapor deposition system using only Argon as carrier gas during the reaction. Extensive characterization of the bulk and exfoliated material confirm that the as-synthesized 2H-WSe2 is layered (i.e., 2D). XRD (X-Ray Diffraction) confirms the phase. At the same time, HRSEM (High-Resolution Scanning Electron Microscopy), HRTEM (High-Resolution Scanning Electron Microscopy), and AFM (Atomic Force Microscopy) clarify the morphology of the material. FIB-SEM (Focused-Ion Beam Scanning Electron Microscopy) estimates the depth of the 2H-WSe2 formation on W foil around 5-8 μm and Raman/UV-Vis measurements prove the quality of the exfoliated 2H-WSe2. The redox processes of Lithium-ion Battery (LiB) studies show an increase in capacity until 500 cycles. On prolonged cycling, the discharge capacity till the 50th cycle at 250 mA/g, the material shows a stable capacity of 550 mAh/g. These observations indicate exfoliated 2H-WSe2 has promising applications as LiB electrode material. References (1) Xia, H.; Xu, Q.; Zhang, J. Recent Progress on Two-Dimensional Nanoflake Ensembles for Energy Storage Applications. Nano-Micro Lett. 2018, 10 (4), 1–30. https://doi.org/10.1007/s40820-018-0219-z. (2) Share, K.; Lewis, J.; Oakes, L.; Carter, R. E.; Cohn, A. P.; Pint, C. L. Tungsten Diselenide (WSe2) as a High Capacity, Low Overpotential Conversion Electrode for Sodium-Ion Batteries. RSC Adv. 2015, 5 (123), 101262–101267. https://doi.org/10.1039/C5RA19717A.