Confined Polysulfide Shuttle by Nickel Disulfide Nanoparticles Encapsulated in Graphene Nanoshells Synthesized by Cooking Oil

Abstract

The polysulfide shuttle effect has remained one of the main obstacles restraining the commercialization of lithium-sulfur battery technology. Herein, we report a yolk-shell structure with nickel disulfide nanoparticles encapsulated in the chemical vapor deposition (CVD)-grown N-doped graphene (NG) nanoshell (termed as NiS2@NG). The synthesis process involves the growth of NG nanoshells simply by annealing Ni nanoparticles in soybean oil vapors without compressed gases, followed by solid-state sulfidation of partially etched Ni nanoparticles. Benefiting from both the physical and chemical confinement mechanisms, the NiS2@NG material exhibits exceptional lithium polysulfide (LiPS) trapping competence (even within a few seconds), as evidenced by visual adsorption and X-ray photoelectron spectroscopy (XPS) analyses. The NiS2@NG cathode demonstrates excellent specific capacity (1213 mA h g-1 at 0.2C current density), good rate capability (by retaining 782 mA h g-1 capacity at 2C current density), and outstanding cycling stability (78% after 100 cycles at 0.5C current density). Moreover, a high sulfur content of 90% is realized with good cycling stability. Besides this, hollow NG nanoshells loaded with sulfur (NG@S) exhibited comparable electrochemical performance but bare NiS2 showed sluggish redox kinetics and poor electrochemical performance due to poor electrical conductivity and the absence of physical confinements. The findings of this study are strongly believed to open up pathways for the development of cathode materials for Li-S batteries.