Delicate Co-Control of Shell Structure and Sulfur Vacancies in Interlayer-Expanded Tungsten Disulfide Hollow Sphere for Fast and Stable Sodium Storage.

Abstract

Hollow multishelled structure (HoMS) is a promising multi-functional platform for energy storage, owing to its unique temporal-spatial ordering property and buffering function. Accurate co-control of its multiscale structures may bring fascinating properties and new opportunities, which is highly desired yet rarely achieved due to the challenging synthesis. Herein, a sequential sulfidation and etching approach is developed to achieve the delicate co-control over both molecular- and nano-/micro-scale structure of WS2- x HoMS. Typically, sextuple-shelled WS2- x HoMS with abundant sulfur vacancies and expanded-interlayer spacing is obtained from triple-shelled WO3 HoMS. By further coating with nitrogen-doped carbon, WS2- x HoMS maintains a reversible capacity of 241.7 mAh g-1 at 5 A g-1 after 1000 cycles for sodium storage, which is superior to the previously reported results. Mechanism analyses reveal that HoMS provides good electrode-electrolyte contact and plentiful sodium storage sites as well as an effective buffer of the stress/strain during cycling; sulfur vacancy and expanded interlayer of WS2- x enhance ion diffusion kinetics; carbon coating improves the electron conductivity and benefits the structural stability. This finding offers prospects for realizing practical fast-charging, high-energy, and long-cycling sodium storage.