Nanosheet-assembled NiS hollow structures with double shells and controlled shapes for high-performance supercapacitors

Hollow micro-and nanostructured materials with controllable shapes are appealing materials for electrochemical energy storage devices with high energy and power densities. Herein, double-shelled hollow nickel sulfides with controlled shape (cube-, ellipsoid-and capsule-shaped) were successfully synthesized by using different morphological alpha-Fe2O3 templates. The as-obtained nickel sulfides have uniform size and well-defined double shells that consist of crossed ultrathin NiS nanosheets. When evaluated as electrode materials for supercapacitors, the capsule-shaped structure exhibits the highest specific capacitance of 1159 F g(-1) at a current density of 2 A g(-)1 due to its high specific surface area (100.2 m(2) g(-1)), low equivalent series resistance (0.80 Omega) and ion diffusive resistance. More importantly, the asymmetric capacitor NiS (capsule-shaped)vertical bar vertical bar RGO@Fe3O4 shows a high energy density of 43.7 Wh kg-at a power density of 664 W kg(-1) (21.8 Wh kg(-1) at 8000 W kg(-1)), and after 5000 charge-discharge cycles, 833% of its capacitance is remained at the current density of 5 A g(-1). (C) 2017 Elsevier B.V. All rights reserved.