Interconnected hierarchical NiCo2O4 microspheres as high-performance electrode materials for supercapacitors.

Herein, interconnected hierarchical NiCo2O4 microspheres (IH-NiCo2O4) were prepared via a solvothermal method followed by an annealing treatment. IH-NiCo2O4 possesses large tunnels and abundant mesopores, which are in favor of their applications in energy storage field. When employed as an electrode material for supercapacitors, IH-NiCo2O4 exhibits a high specific capacitance of 1822.3 F g-1 at a current density of 2 A g-1, an excellent rate property of 68.6% capacity retention at 20 A g-1, and an 87.6% specific capacitance retention of its initial value after 7000 cycles at a high current density of 10 A g-1, superior to those of IH-Co3O4. Furthermore, an optimal asymmetric supercapacitor (ASC) was also constructed with IH-NiCo2O4 as the positive electrode and graphene as the negative electrode. The ASC delivers a high energy density of 39.4 Wh kg-1 at a power density of 800 W kg-1. Even at a high power density of 8000 W kg-1, the energy density still reaches 27.2 Wh kg-1. Moreover, the ASC shows a good cycling stability with 80.1% specific capacitance retention after 5000 cycles at 6 A g-1. The excellent electrochemical performance of IH-NiCo2O4 makes it a promising electrode material in energy storage field.