Electrochemical Properties of Carbon-Coated SnO2-Graphene Nanocomposites for Rechargeable Lithium-Ion Batteries

SnO₂ nanoparticles were carbon-coated using two different methods and then dispersed on the reduced graphene oxide nanosheets prepared from modified Hummer’s method. Carbon-coating was performed by a solvothermal method from glucose precursor material or by carbonization in Polyacrylonitrile (PAN) based carbon fibers.The later was prepared by dispersing SnO₂ nanoparticles in N-Methyl-2-pyrrolidone and then the dried powder was stabilized in air at 270°C for 30 minutes followed by the heat treatment at 900°C for 2 hours. The coated nanocomposites were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. From TEM observations, it was found that the SnO₂ nanoparticles were 2-6 nm in diameter and were uniformly distributed on the reduced graphene oxide nanosheets. Electrochemical properties were evaluated by galvanostatic charge-discharge cycling. Carbon-coated SnO₂-reduced graphene oxide nanocomposites showed higher capacity and more stable electrochemical performances than non-coated SnO₂-reduced graphene oxide nanocomposites. Carbon coating enhances the conductivity of the electrode and it reduces the stress developed by the volume changes of the SnO₂ nanoparticles during charge/discharge cycles. The synergistic effect of the amorphous carbon, SnO₂ nanoparticles and reduced graphene oxide nanosheets is also responsible for the superior specific capacity of carbon-coated anode material.  Excellent rate capability and cyclic performances were also demonstrated with higher current densities of 500 and 1000 mA/g.