Preparation And Performance Study Of NiO/Graphene Composites As Supercapacitor Material

Supercapacitors have been recognized as unique energy storage devices whichhave higher energy density than conventional capacitors, and higher power densityand longer cyclic life than batteries, filling the gap between the rechargeablebatteries and the typical dielectric capacitors. Supercapacitors have been used inindustrial UPS power supply, electric vehicle, aerospace and so on. The researchesabout supercapaacitors are mainly concentrated on high performance electrodematerials. In this paper, different structured NiO/graphene composites weresynthesized, and the preparation processes and electrochemical performances werestudied in detail.(1) The flower-like NiO/graphene composites were synthesized by a refluxingmethod in the presence of graphene, the amount of NiO loaded is adjusted bycontrolling the refluxing times. The3-dimensional composites possessed improvedelectrochemical performance and high specific capacitance. At the electric currentdensity of200mA/g, the discharge specific capacitance of the obtained compositematerials was about687.6F/g. This capacitance is very impressive by comparisonwith pure NiO, which owns only276.4F/g at the same conditions. The capacityretention of90.8%can be maintained after2000continuous charge-discharge cycles,demonstrating its promising potential to be used for supercapacitors.(2) The solvothermal method was used to synthesize octahedral NiO/graphenenanocomposite, in which graphene conducted as conductive matrix and octahedralNiO were grown on the surface of graphene sheets (GNS). The size of theas-prepared octahedral NiO could be tuned by varying the sintering time. And thesurfactant (CTAB), GNS and solvents were shown to play critical roles in theformation of octahedral NiO/graphene. Then the material was tested with XRD,SEM and TEM etc, the results reflected that the composite with novel structure showed excellent structural stability. The capacity retention is about95.2%after1000cycles at current density of200mA/g.(3) The hydrothermal method is an important method for nanomaterials. Theflower-like porous NiO/graphene was synthesized by hydrothermal method withmixed glycerol and DI-water solvents, and characterized by SEM, TEM, XRD, BETand so on. Then the electrochemical performances of the obtained compositematerials were studied by CHI660C. It shows that the discharge specific capacitancewas about413F/g at the current density of200mA/g. When galvanostaticcharge/discharge at current density of1A/g, the capacity retention is89.8%after2000cycles.