Stabilising Cobalt Sulphide Nanocapsules with Nitrogen-Doped Carbon for High-Performance Sodium-Ion Storage

• Published in: Nano-micro letters 2020-02, Vol.12 (1), p.48-48, Article 48
• Main Authors: Wu, Yilan, Gaddam, Rohit R., Zhang, Chao, Lu, Hao, Wang, Chao, Golberg, Dmitri, Zhao, Xiu Song
• Format: Article
• Language: English
• Subjects: Anodes; Cages; Capacitors; Carbon; Cobalt sulfide; Cobalt sulphide; Core–shell structure; Electrode materials; Electrodes; Electrolytes; Electron conductivity; Encapsulation; Engineering; Graphene; Ion storage; Ion transport; Nanoparticles; Nanoscale Science and Technology; Nanotechnology; Nanotechnology and Microengineering; Nitrogen; Nitrogen-doped carbon; Sodium; Sodium-ion capacitors; Storage capacity; Sulfides
• ISSN: 2311-6706; 2150-5551
• DOI: 10.1007/s40820-020-0391-9

Highlights Cobalt sulphide nanoparticles are encapsulated in nitrogen-rich carbon cages via a simple and scalable method. Insight into sodium storage mechanism is systematically studied via in situ TEM and XRD techniques. The sodium-ion capacitor device achieved high energy densities of 101.4 and 45.8 Wh kg −1 at power densities of 200 and 10,000 W kg −1 , respectively, holding promise for practical applications. Conversion-type anode materials with a high charge storage capability generally suffer from large volume expansion, poor electron conductivity, and sluggish metal ion transport kinetics. The electrode material described in this paper, namely cobalt sulphide nanoparticles encapsulated in carbon cages (Co 9 S 8 @NC), can circumvent these problems. This electrode material exhibited a reversible sodium-ion storage capacity of 705 mAh g −1 at 100 mA g −1 with an extraordinary rate capability and good cycling stability. Mechanistic study using the in situ transmission electron microscope technique revealed that the volumetric expansion of the Co 9 S 8 nanoparticles is buffered by the carbon cages, enabling a stable electrode–electrolyte interface. In addition, the carbon shell with high-content doped nitrogen significantly enhances the electron conductivity of the Co 9 S 8 @NC electrode material and provides doping-induced active sites to accommodate sodium ions. By integrating the Co 9 S 8 @NC as negative electrode with a cellulose-derived porous hard carbon/graphene oxide composite as positive electrode and 1 M NaPF 6 in diglyme as the electrolyte, the sodium-ion capacitor full cell can achieve energy densities of 101.4 and 45.8 Wh kg −1 at power densities of 200 and 10,000 W kg −1 , respectively.