| :Lithium-ion battery (LIB) as a clean energy battery, can solve the problems of energy and environment effectively, especially its applic-ation for electric vehicles in the future. SnO2/graphene composites as the anode of LIBs, have excellent electrochemical performances after a com-bination of the high capacity for SnO2and outstanding physical performa-nces for graphene. In the work, starting from graphite oxide (GO), experimentally, we prepared SnO2/graphene composites by hydrothermal method, after that, the products modified by heat treatment and carbon-coated, and its organizations, structures characterized by XRD, SEM, FTIR, Raman spectra, TEM and HRTEM, finally, their electroche-mical performances tested; Theoretically, we studied the structure of GO and explained the experimental XRD pattern of reduced graphene oxide(rGO) via computer simulation with WB equation. The main innovative conclusions are summarized as follows:1. GO has the turbostratically stacked structure and carbon atoms(CAs) have higher thermal vibration displacement(HTVD) in it, which caused by oxygenated functional groups(OFGs) and defects. The OFGs increase the vibration-frequency of C=C for CAs, which leads to the blue shift in FTIR and Raman spectras for GO when compared with graphite(G). The defects weaken the binding force among CAs and cause the displacement of CAs’equilibrium positions, which leads to the higher HTVD of CAs and reduces the thermal stability of GO, such as, in this work compared with G, the starting oxidization-temperature-point of carbon decreases by145.6℃in GO-2.2. The XRD results demonstrate that the relative degree of oxidation for GOs can be characterized by (001) diffraction peaks, when GO with the biggest interlayer distance and the strongest intensity (i.e. defects are the lowest) for (001) diffraction peak is the best precursor for the preparation of rGO. The transition state GO-1is made up of turbostratic graphite nanosheets with different layers and GO nanosheets with different interlayer distances and layers, generated in the process from G to GO.3. Theoretically, graphene does not have (002) diffraction peak in the XRD pattern, but in fact rGO has it, which caused by its reunite. Experimentally, the position of (002) peak for rGO is next to but lower than G’s, such as, in our work, the gap is1.62°for them, which attributed to its fewer number of graphene layers that has been demonstrated by the effect of the number of layers on the peak via computer simulation, while rGO mainly made up of3number graphenes by comparation of the theoretical and experimental results.4. In the SnO2/rGO composites, SnO2particles are well-distributed on the rGO surface, and the size diminished by rGO and it just has ahout5nm in the calcined product, SnO2-rGO-2composites. The carbon-coated SnO2/rGO composites, amorphous carbon are well-coated on the surface of the composites, and TEM showed that the C-SnO2-rGO-2composites made up of low amount-carbon sections and higher amount-carbon-group sections. The electrochemical testing demonstrated that rGO evidently improves the performance of SnO2. At the current density lOOmA/g, the results show that the higher-content-rGO sample, SnO2-rGO-2has the most excellent performance with charge specific capacity791mAh/g and discharge specific capacity799mAh/g after100cycles, close to the theoretical value of SnO2790mAh/g. After lower-content-rGO and poorer-performance sample SnO2-rGO-1coated by carbon, the product with higher-content-carbon sample C-SnO2-rGO-2shows the exceedingly good cyclical stability, which has the charge specific capacity288mAh/g after150cycles and achieves67%of the initial capacity. |
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