Hierarchical nickel nanowire@NiCo2S4 nanowhisker composite arrays with a test-tube-brush-like structure for high-performance supercapacitors

Well-ordered, hierarchical and nanostructured composite electrodes have gained tremendous research attention for energy storage applications, because of their highly efficient electron and ion transport channels and abundant electrochemically active sites. However, it still remains a great challenge to prepare such architectures on a large scale with high active material mass loadings for making better use of the whole electrode area. Herein, needle-like NiCo2S4 nanowhiskers are radially grown on a uniform nickel nanowire array (NNA), forming a unique densely packed test-tube-brush-like nanostructure. Since these NiCo2S4 nanowhiskers are intrinsically highly electrically conductive, the hierarchical electrode structure can drastically elevate the charge transport ability in the whole electrode region; additionally, it can greatly help to release stresses at micro- and nano-scales, leading to robust mechanical flexibility and superior energy storage capability. Experimental results show that this composite array electrode exhibits an ultrahigh specific capacitance of 1523 F g−1 at a mass loading of 4.03 mg cm−2 at a current density of 1 A g−1, and a rate capability of 61.8% from 1 to 40 A g−1, together with a superior cycle stability with 92.4% capacitance retention after 20 000 cycles at a current density as high as 10 A g−1. An asymmetric supercapacitor consisting of a NNA@NiCo2S4 (NNANCS) cathode and activated carbon (AC) anode delivers a maximum energy density of 47.29 W h kg−1 at a power density of 793.5 W kg−1 and still delivers an energy density of 29.50 W h kg−1 at a maximum power density of 27.64 kW kg−1. This work may inspire new ideas for constructing high-performance electrodes for energy storage.