Hierarchically urchin-like hollow NiCo₂S₄ prepared by a facile template-free method for high-performance...

Hollow structures draw much attention for high energy density supercapacitors due to their large hollow cavities, high specific surface area, and low interfacial contact resistance. However, constructing hierarchical hollow structures remains a challenge. Herein, we reported a facile template-free method for a novel urchin-like hollow nickel cobalt sulfide (NiCo₂S₄). The hollow interior and urchin exterior remarkably improved the specific capacitance and accommodated structural collapse caused by electrochemical reactions. Owing to these features, the urchin-like hollow NiCo₂S₄ spheres exhibited an impressive capacitance of 1398F g^-1 at 1 A g^-1 and maintained 1110F g^-1 with a large current density of 10 A g^-1. The hybrid supercapacitor fabricated by NiCo₂S₄ and active carbon possesses an energy density of 39.3 Wh kg^-1 at a power density of 749.6 W kg^-1 and an outstanding cycling stability of 74.4% retention after 5000 cycles. Our work presents a facile method of constructing a hollow structure of binary sulfide materials and also makes progress on highly efficient supercapacitors.