Abstract: A core-shell structure of the carbon-coated natural graphite oxide composite was successfully prepared. Natural graphite was initially oxidized using concentrated sulfuric acid and then carbon coated by the carbonization of phenolic resin at high temperature. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman techniques were used to characterize the morphology and structure of the natural graphite materials before and after oxidation and carbon coating by the pyrolysis of the phenolic resin. The results showed that the surface of the natural graphite particles became smoother and the surface defects were effectively modified after oxidation and carbon coating. The electrochemical test results showed that the electrochemical performance of the natural graphite improved significantly by oxidation with sulfuric acid and by carbon coating. When the covering amount of phenolic resin was 9% the modified natural graphite material gave the best electrochemical performance. Its initial discharge capacity was 434.0 mAh·g^-1 and it remained 361.6 mAh· g^-1 after 40 charge-discharge cycles. The discharge capacity of the untreated natural graphite was only 332.3 mAh·g^-1. The modification approach that improved the capacity of the natural graphite effectively is of great significance for the application of natural graphite in lithium ion batteries.

Key words: Anode material, Natural graphite, Phenolic resin, Oxidation, Coating