Self-assembled NiCo2O4 microspheres for hybrid supercapacitor applications

Hierarchical NiCo2O4 microspheres self-assembled by nanorods, nanosheets and nanoparticles were prepared through hydrothermal and calcination processes. By changing solvents and/or additives during hydrothermal process, the nanostructures in NiCo2O4 microspheres were regulated. Among the as-prepared samples, nanosheets-assembled NiCo2O4 microspheres (NCO-S) exhibited the highest specific capacitance of 667.6 F g(-1) at current density of 1 A g(-1) and possessed good cycling stability of 85.2% capacity retention rates for 3000 cycles. The excellent electrochemical performance was attributed to its hierarchical nanostructures, high specific surface area and improved electric conductivity. Furthermore, the hybrid supercapacitor with NCO-S as positive electrode and reduced graphene oxide as negative electrode delivered a prominent energy density of 26.2 Wh kg(-1) at power density of 920.8 W kg(-1) and excellent capacity retention of 99.4% for 5000 cycles.