Hierarchical Ni-Co layered double hydroxide nanosheets on functionalized 3D-RGO films for high energy density asymmetric supercapacitor

In this paper, ultrathin reduced graphene oxide films on nickel foam were fabricated via a facile dip-coating method combined with thermal reduction. Hierarchical Ni-Co layered double hydroxide nanosheets with network structure were electrodeposited on the ultrathin reduced graphene oxide films in a simple three-electrode system. The thickness of Ni-Co layered double hydroxide nanosheets can be controlled through adjusting the deposition temperature. The as-prepared electrode exhibited excellent electrochemical performance with specific capacitance of 1454.2 F g−1 at a current density of 1 A g−1. An asymmetric supercapacitor device was designed with the as-prepared composites as positive electrode material and Nitrogen-doped reduced graphene oxide as negative electrode material. This device could be operated in a working voltage range of 0-1.8 V in 1 M KOH aqueous electrolyte, delivering a high energy density of 56.4 W h kg−1 at a power density of 882.5 W kg−1. One supercapacitor can power two LEDs with rated voltage of 1.8-2.0 V. After 10,000 consecutive charge-discharge tests at 10 A g−1, this asymmetric supercapacitor revealed an excellent cycle life with 98.3% specific capacitance retention. These excellent electrochemical performances make it become one of most promising candidates for high energy supercapacitor device.