Fabrication of urchin-like NiCo2(CO3)1.5(OH)3@NiCo2S4 on Ni foam by an ion-exchange route and application to asymmetrical supercapacitors

Pseudocapacitor electrode materials, such as transition metal oxides/sulfides, have been extensively investigated and shown to have fast energy storage properties, but their low rate performance and poor cycle stability are serious problems in practical applications. We present here a design for the architecture of these electrode materials with the aim of improving the rate performance and cycle stability of pseudocapacitors by using an interface ion-exchange method. Precursor materials obtained by a hydrothermal reaction were soaked in aqueous NaHS solution to synthesize the urchin-like core–shell structure of NiCo2(CO3)1.5(OH)3@NiCo2S4. Such core–shell nanostructure electrode materials can make full use of both components with synergistic effects. Excellent results were obtained with a capacitance of 956.4 F g−1 at a current density of 4 A g−1 in the three-electrode system and an actual energy density of 32.3 W h kg−1 and power density of 1835 W kg−1 in the asymmetrical supercapacitor.