SnO₂/Graphene Nanocomposite As Anode Material For Lithium-ion Batteries

SnO₂/graphene nanocomposite as objects of the research, focusing studies on thespecific capacity, cyclability and rate capability of materials, the SnO₂/graphenenanocomposite was prepared using hydrothermal synthesis method, and characterized byvarious electrochemical methods in combination with Infrared（FTIR） spectroscopy, X-raydiffaction（XRD）, Brunauer-Emmer-Teller（BET） surface area measurement, ScanningElectron Microscope（SEM）, Transmission Electron Microscop （TEM）, Ramanspectroscopy, Electrochemical Impedance Spectra（EIS） and Cycle voltammetry（CV）.Nansoized SnO₂powders were successfully prepared by hydrothermal synthesis methodusing SnCl2·2H2O as starting material and ethanol as solvent. Results indicate that ethanolprevent Cl-from access to tin Sn4+due to steric effect and hence increase the stability ofthe solution. Ethanol not only as a complex agent to form a polymer network but also as a"spacer" to modulate the distance between metal-ions, preventing metal oxide particlesfrom aggregation. The structure of nanosized SnO₂powder was studied. The experimentshows that SnO₂nano-particles which prepared by SnCl2·2H2O in alkaline ethanolsolution （pH≈12）120℃under6h has a large spatial structure and specific surface area.The initial discharge capacity of1773mAh/g was found at a rate of0.1C in a potentialrange0.005V-3.0V, and a stable capacity of582mAh/g was found even after30cycles.Nansoized SnO₂powders as lithium-ion battery anode material has high specific capacityand good cycle performance.The graphene was prepared by microwave from graphite oxide which was synthesizedby means of modified Hummers’ method. The structure, morphology and electrochemicalproperties of graphene were studied. Graphene electrode was test in different currentdensities. The initial discharge capacity of2300mAh/g was found at a rate of0.1C and astable capacity of547mAh/g was obtained even after30cycles. Coulomb efficiency is95%. This indicates that the graphene electrode has a high capacity in initialcharge/discharge, but it has no good cycle stability. It is shown that the higher decay rateis a key factor which affects the life cycle life. SnO₂/graphene composites were prepared by hydrothermal synthesis method and themolar ratio of SnO₂/graphene is3:1. The composition, structure and morphology as wellas electrochemical properties were studied. It suggests that SnO₂is uniformly distributedover the surface of GNS, which is because that the oxide anions in SnO₂could havebridged with GNS surface species to result in good spreading between SnO₂and GNS.The initial discharge/charge capacity is2646mAh/g and1442mAh/g, discharge/chargecapacity is1160mAh/g and1113mAh/g at a rate of0.1C, respectively and also theCoulombic efficiency keeps more than96%after30cycles. When the current densityincreases up to2C and5C, and the Coulombic efficiency keeps more than98%after the30cycles, respectively. These results show that SnO₂/graphene composite has goodreversible capacities, rate capacity and cyclability. Because SnO₂anchored on the surfaceof GNS, a new active surface site is created, the activation energy of Li+transport processis significantly reduced, and the transport process of Li+across the interface is accelerated,which leads to the improvement of cycle ability and rate capability of SnO₂/graphenecomposite.The phenomena of specific capacity that is lager than the sum of the capacities of SnO₂and GNS suggest the presence of synergistic interaction between the two consituents.SnO₂/graphene composite was evaluated by cycle voltammetry in different cycles. ACimpedance was used to examine the bare SnO₂and SnO₂/graphene composite. The chargetransfer resistance for SnO₂/graphene composite has been obtained by fitting the software,and exchange current density has been calculated.It is found that there is a synergetic effect in SnO₂/graphene composite.