Preparation And Energy Storage Properties Of Graphene Based Cobalt Oxide Nanocomposites

Lithium-ion batteries and supercapacitors, important energy storage devices, are in great demand of applications in electronic devices and vehicles. With the development of society, requirments for electrochemical performance of energy storage equipment increase day by day. This greatly arouse the passion of designing lithium-ion batteries and electrochemical capacitors with excellent performance which is mainly determined by the electrode materials. Cobalt oxide (such as Co3O4, CoO and Co(OH)2), one of important electrode materials, can be applied in lithium-ion batteries and supercapacitors. Although possessing high theoretical capacity, cobalt oxide’s poor electrical conductivity and large volume change lead depressively to a quick capacity decay during cycling. Although lots of researches on energy storage have been reported, currently, cobalt oxide can’t satisfy the demand of applications in electronic equipment and electric cars. To improve the electrochemical properties of cobalt oxide, this paper designs the preparation of cobalt oxide/graphene nanocomposite, and focuses on change principle of morphology and structure of the composite as well as interface interaction between the components. And then we test the electrochemical performance and study the key factors that affect the electrochemical performance.We use a facile precipitation approach to synthesize cobalt hydroxide/graphene composites (Co(OH)2/GNS). The Co(OH)2nanoplates, β-Co(OH)2, with interesting hexagonal patterns of average size of about130nm and average thickness of about20nm, stand vertically on the surface of graphene sheets, and the preferable growth face is (001), which is perpendicular to graphene. The Co(OH)2are connected to graphene by Co-C covalent bond. When applied as anode for lithium ion batteries, the initial discharge capacity at50mA/g is1686.0mAh/g, the initial reversible charge capacity is976.5mAh/g, the reversible capacity after50cycles is1103mAh/g。 The initial discharge capacity and charge capacity at1A/g is496.1mAh/g and449.4mAh/g, respectively.Next, the prepared Co(OH)2/GNS were annealed to make porous cobalt oxide/GNS composite at the range of300-500℃. Cobalt oxide/GNS composite have interesting hexagonal sheets of average size of50-100nm, with holes on it. The composite made at500℃have the best electrochemical performance. The initial discharge capacity at50mA/g is1015.5mAh/g, and the capacity after60cycles is1398.7mAh/g.Meanwhile, we can regulate and control the morphology and structure of cobalt hydroxide/graphene composite by doping aluminum element, and study the influence of aluminum content on morphology, structure and electrochemical properties of the composite. When the molar ratio of Co/Al is2:1, uniform hexagonal nanosheets are anchored on graphene and the composite’s electrochemical performance are best with highest specific capacitance of675.7F/g at the current density of0.1A/g.In addition, cobalt oxide/GNS composite were prepared by insitu pyrolytic of Co(NO3)2/GNS. Cobalt oxide, made at temperature higher than200℃,30-50nm in diameter, are homogeneously anchored on graphene and connected to graphene by Co-O-C covalent bond. The results show that cobalt oxide/GNS made at200℃present the best electrochemical performance, with specific capacitance of540F/g after500cycles at the current density of0.1A/g.