Preparation Of Graphene-Based Materials And Their Lithium Storage Performance

Lithium-ion batteries are the most popular secondary batteries because of their superiorelectrochemical porperties, safety, and environmental friendly. However, the energy densityand power density of lithium-ion batteries cannot fulfill the increaing demand of productionand livelihood as the electric vehicle industry is growing and the protable devices are moreand more porpular and versatile. Graphene is a type of carbon material which is one carbonatom thick lattice with a honeycomb network. Because of its high electronic conductivety,large specific area, high tensile strength, thermostablity and chemical resistance, it is greatsignificant in the research and applying of graphene in electrode material for lithium-ionbatteries. Graphene based electrode materials usually possess large specific capacity, longcycle life, and excellent rate capability. Graphene based electrode material is promising andwould be expected to largely increase the energy density and power density of lithium-ionbatteries.Firstly, the a novel anode material for lithium-ion batteries, tin nanoparticles coated withcarbon embedded in graphene (Sn@C/graphene), was fabricated by hydrothermal synthesisand subsequent annealing. The structure and morphology of the nanocomposite werecharacterized by X-ray diffraction, scanning electron microscopy, and high-resolutiontransmission electron microscopy. The reversible specific capacity of the nanocomposite is~662mAh g-1at a specific current of100mA g-1after100cycles, even~417mAh g-1at thehigh current of1000mA g-1. These results indicate that Sn@C/graphene possesses superiorcycle performance and high rate capability. The enhanced electrochemical performances canbe ascribed to the characteristic structure of the nanocomposite with both of the graphene andcarbon shells, which buffer the volume change of the metallic tin and prevent the detachmentand agglomeration of pulverized tin.It is great significant for studying the impact factors on lithium storage of graphenebecause it is important for research and development of graphene-based and evencarbonaceous electrode materials. Various hydrothermal reduced grpahene were synthesizedfrom graphene oxide, including non-doped, nitrogen-doped, and boron-doped graphene.X-ray photoelectron spectroscopy, Raman spectrum, elemental analysis, and specific areaanalysis were employed for sample characterization, which indicated that hereroatoms wereintroduced in the graphene structure and created a certain amount of defects, vacancies andcaverns.The electrochemical performances of the samples indicated that the doped graphene deliver larger specific lithium storage due to the defects, vacancies and caverns which werefavorable for the lithium absorption and diffusion. For the heteroatoms impact, boron atomsare more benefical than nitrogen atoms for enhancing the lithium storage in graphene. Theoxygen containing groups can not only introduce defects, vacancies and caverns but alsointeract with the lithium-ion. Therefore, graphene oxide which including a large amount ofoxygen containing groups dilevered the largest specific capacity. The graphene with largerspecific area possesses more lithium storage sites but enhancing the specific area is noteffective for enhancing the lihium storge comparing with heteroatoms and oxygen containinggroups.