Preparation Of SnO₂/Graphene Composite And Synergistic Effect

The electrochemical performance of SnO₂/graphene nanocomposites（SG） andsynergistic effect between SnO₂and graphene existing in the SG nancomposites are the mainobjects of this work. The structures and morphologies of the synthesized nanocompositeswere studied using Scanning Electron Microscope（SEM）, Transmission ElectronMicroscope （TEM）, X-ray diffraction（XRD）, Infrared（FTIR） spectroscopy,Brunauer-Emmer-Teller（BET） surface area measurement, while its electrochemicalperformances were tested by Electrochemical Impedance Spectra （EIS）, Cyclevoltammetry（CV） and glanostatic discharge/charge test instrument. The synergistic effectbetween SnO₂and graphene of SnO₂/graphene nanocomposites was confirmed.SnO₂nanopowders were successfully synthesized through solvent-thermalsynthesis method by the reaction between SnCl2ethanol solution and NH3·H2O. Ethanolwas choosed as solvent instead of water. The characterizations of SnO₂nanopowdersindicate that when the solution pH value is close to3the resultant product comes out to benanocrystal. The initial discharge capacity of1888mAh/g was gained at a rate of0.2C（the theoretical capacity of SnO₂is782mAh/g） in a potential range0.01V-3.0V, and astable capacity of663mAh/g was found after30cycles. The capacity retention rate is48%.Graphene nanosheets （GNS） with carboxylic acid, phenol hydroxyl and epoxidegroups were prepared by microwave-induced exfoliation of graphene oxide （GO） whichwas synthesized by means of ultrasound-assisted modified Hummers’ method. Results ofFTIR show that large portion of oxygen-containing functional groups was removed fromGO via microwave-heating GO. Discharge/charge cycling of GNS electrode was carriedout at different current densities in the voltage of0.01V-3.00V and the initial dischargecapacity of2468mAh/g was gained at a rate of0.2C（according to the theoretical capacityof SnO₂） and the stable capacity was kept at604mAh/g after30cycles. The capacityretention rate is37%. The GNS anode shows a high capacity in initial discharge, butcapacity retention still needs to be enhanced. SnO₂/graphene nanocomposites（SG） were assembled via adding GNS to SnCl2ethanolsolution during the alcoholysis process. The morphology characterization indicates thatSnO₂nanoparticles grown this way were anchored selectively at the surface of GNS,owing to the intimate interactions between functional groups of GNS and SnO₂nanoparticles. The EDS analysis of the nanocomposites surface indicates that the molarrate of SnO₂:GNS is close to3:1.The initial discharge capacity is2467mAh/g at a rate of0.2C and the capacity of869mAh/g was till conserved after30cycles, meanwhile theColumbic efficiency keeps more than98%, and he capacity retention rate is35%.Compared the discharge capacity of the SG nanoparticls used as anode with thecalculated value which was obtained in the light of composite ratio of SnO₂and GNS,synergistic effect exists in the cyclic process at various current densities. The phenomenashould be related to the interactions between SnO₂and GNS substrate, in which theflexible GNS with super conductive capability parcels isolated SnO₂particles to restrainthe volumetric expansion and aggregation during discharge/charge cycles as well asimproves the poor electron conductivity of SnO₂particles.The electrochemical performance of （as-prepared nanoparticls） SnO₂, graphene andSG were evaluated by cycle voltammetry and EIS respectively after10cycles.