One-step controlled synthesis of hierarchical hollow Ni3S2/NiS@Ni3S4 core/shell submicrospheres for high-performance supercapacitors

Composition and microstructure are two main factors for enhancing the specific capacity, rate capability, and cycling life of electrode materials in electrochemical energy storage devices. Here, size-tunable hierarchical hollow core/shell submicrospheres based on nickel sulfide are for the first time rationally designed and synthesized through a one-step hydrothermal route, in which Ni3S2/NiS hollow submicrosphere works as a core and Ni3S4 nanoflakes as shells. The diameter of the hierarchical sphere can be controlled by cetyltrimethyl ammonium bromide. The formation mechanism of this unique structure is systematically investigated, which can be attributed to the combined action of cage effect, Kirkendall effects and Ostwald ripening mechanism. Due to the synergistic effects of various phase nickel sulfide, such hybrids exhibit superior electrochemical performance. When served as electrodes for supercapacitors, the hybrids show a high specific capacity of 1031.3 Cg(-1) at a current density of 2 Ag-1. Even as the current density increases to 40 A g(-1), the hierarchical core-shell nanosphere still reserves 614.4 C g(-1), exhibiting an excellent rate capacity and a good capacitance retention of 90.3% after 3000 cycles at 10 A g(-1). Furthermore, asymmetric supercapacitor based on the Ni3S2/NiS@Ni3S4 hybrid and reduced graphene oxide shows high power density, high energy density and long cycling lifespan. (C) 2018 Elsevier Ltd. All rights reserved.