| Carbon has many allotropes, the sp3 hybridization diamond, sp2 hybridization graphite and sp hybridization acetylene are the three most famous crystal allotropes in all the carbon materials. The founds of fullerene in 1985, carbon nanotube in 1991, and single-layer graphene in 2004 have expanded the allotropes of carbon materials and induced the revolution in nanoscience and nanotechnology. Graphene is the ideal two-dimensional structure, formed by a layer of sp2 hybridization of carbon atoms. The carbon atoms are connected each other by a strongσbonds; each carbon atom has contributed a no-bondedπelectron andπorbit can be formed at the perpendicular direction toπelectron. Graphene and its derivatives may have applications in electronic, mechanics, optical, thermology, field-emission and energy storage. Especially, graphene has potential application in lithium ion rechargeable battery as anode material, which has good cycle behavior. Tin oxide has attracted much attention for its high capacity as anode material for lithium ion battery material; however, the cycle behavior is poor. To get anode material for lithium ion material with high capacity and good cycle behavior, we synthesized the composites of graphene and tin oxide nanocrystals. Chemical reduction of graphene oxide is a good approach to produce graphene with lower cost and larger scale. In this paper, we have synthesized the composites of graphene and tin oxide nanocrystals and investigated the properties of composites as anode material for lithium ion battery.In the first part, we synthesized the graphene and investigated the properties of graphene. The graphite, NaNO3, H2SO4, and KMnO4 were used as row materials to synthesize graphene oxide. The produced graphene oxide have many oxygen functional groups and defects, which induce the bigger distance of carbon layer and lower Van der Waals force. By ultrasonic route, the single-layer and sevral-layer graphene oxide can be achieved. After the reduction of graphene oxide by hydrazine to remove the oxygen functional group, graphene was produced. To investigate the structure of as-prepared graphene, we characterized the sample by XRD, SEM, TEM and Raman. XRD patterns of graphite and graphene oxide show that compared to graphite, the 2θof diffraction peak of in graphene oxide becomes smaller, indicating that the bigger distance of carbon layer in graphene oxide. Compared to XRD pattern of the graphene oxide, the diffraction peak of (002) crystal plane is at higher 2θin XRD pattern of graphene, which shows that the distance of carbon layer becomes smaller, however, the distance is still bigger than that in graphite. The XRD pattern of graphene shows that the reduction of graphene oxide by hydrazine is not complete and oxygen functional groups and defects are still existed in graphene. The morphology of produced graphene and graphene oxide are thin and waved sheets, many folds can be observed in the graphene nanosheets. In TEM images, we can also observe layered structure in graphene with a few layers. In Raman spectrum, the ID becomes more intenser in graphene oxide than that in graphite, which shows that strong oxidization destroy the regular arrangement in layer of graphite, many oxygen functional groups, dangling bonds and defects appeared, the hybridization of carbon was transformed from sp2 to sp3. The degree of crystallinity of graphite has been lowered. However, after reduction of graphene oxide to graphene, the intensity of ID becomes weaker than IG, which shows the reduction process increased the degree of crystallinity of graphene and the regular of arrangement. The results from Raman spectrum are in accordance with XRD patterns.In the second part of this paper, we synthesized SnO nanocrystals. By Schlenk line, SnCl2 as row material, the tin hydroxide was first produced, and then this intermediate Sn6O4(OH)4 decomposed to SnO nanocrystals. XRD and SAED analysis shows that, the crystal structure of as-prepared sample is tetragonal SnO, and the wide and weak diffraction peaks show the small size of SnO nanocrystals. The morphology of SnO nanocrystal is nanoflower, which is formed by aggregation of a few smaller SnO nanoparticles. The size of nanoflowers is about 50 nm, and nanoflowers have uniform size distribution.In the third part, GNS/SnO composite was synthesized and its properties were investigated. We abtained the mixture of the GO and SnO nanocrystals firstly, and then GO was reduced to GNS with adding hydrazine dropwise. By TEM images, we can see that we have successfully synthesized the composites of GNS/SnO, SnO nanocrystals were absorbed at the surface of GNSs. The morphology of GNS is not changed in this process. The diffraction peak of (002) crystal planes in GO is at 2θ=10.8°, indicating the bigger interplanar distance. The bigger interplanar distance was induced by many oxygen functional groups and defects on the surface of GO. After the reduction to GNS by hydrazine, the diffraction peak of (002) crystal planes moves to 2θ=23°, which is still bigger than that in graphite. The interplanar distance becomes smaller, which is bigger than 0.34 nm. In the XRD patterns of GNS/SnO composites, we can observe clearly these diffraction peaks of tetragonal SnO and the diffraction peak of GNS at about 20°. All the experimental proof shows that we have successfully synthesized the composites of GNS/SnO. Based on the intensity of G peak and D peak of sample in Raman, we investigated the structure of composites. ID/IG is bigger than one in graphene oxide, the structure of graphene oxide is irregular. ID/IG becomes smaller than one in graphene, the regularity of carbon layer was improved. However, the ID/IG becomes bigger than one in the Raman spectrum of composites of GNS/SnO, the regularity was destroyed in the compositing process. The results from Raman spectrum are similar to XRD and TEM. We investigated the vibration of C=O and C-O in sample by FR-IR spectrum. The intensity of vibration of C=O and C-O in composites of GNS/SnO becomes weaker than that in graphene oxide, which shows the reduction process from graphene oxide to graphene, the results are similar to that got by XRD and Raman spectrum. In the end, we investigated the properties of GNS/SnO composites as anode material for lithium ion battery, which showed potential application as anode material. The GNS/SnO composites keep the advantages of SnO nanocrystals and GNS as anode materials, respectively. The GNS/SnO composites have high charge capacity and stable cycle behavior as anode material for lithium ion battery, which is a good choice as anode material for lithium ion battery.
|
PDF Full Text Request