Effects of modification on performance of natural graphite coated by SiO2 for anode of lithium ion batteries

A stable silicon dioxide film was coated on the surface of natural graphite anode by sol-gel method with Si(OCH2CH3)4, and effects of modification on performance of natural graphite were investigated. The structure and properties of graphite samples were determined by X-ray diffractometry(XRD), scanning electron microscopy(SEM), energy-dispersive X-ray spectroscopy(EDS) and electrochemical measurements. The modified graphite shows mainly the layer structure, and silicon dioxide film is amoiphous. Compared with the pure natural graphite, the modified graphite exhibits the higher specific capacity of 366 mA.h/g. After 40 charge-discharge cycles, the capacity retention ratio of the modified graphite reaches 99.55%, while that of natural graphite is only 83.04%. The results indicate that the surface modification of natural graphite by SiO2 is effective for improving the electrochemical performance of the natural graphite anode for lithium ion batteries.