Carbon nanofibers were prepared by the exfoliation of natural graphite flake in a propylene carbonate solution containing a lithium salt and sonication. The electrochemical behavior of the carbon nanofibers used as the negative electrode in lithium-ion batteries was investigated. Carbon nanofibers heat-treated at 600 °C had a diameter of several tens of nanometers. From X-ray diffraction measurements and Raman spectroscopy, it was found that a graphitic structure derived from natural graphite flake remained in the carbon nanofibers. Carbon nanofibers heat-treated at 400 °C showed a higher reversible capacity than NG-7 (natural graphite powder) and a rapid response in the cyclic voltammogram. This is on account of the nanosize effect. The best electrochemical performance among all the carbon nanofibers was obtained by heat treatment at 400 °C. The rate performance of the carbon nanofiber heat-treated at 400 °C was also examined.
2013 The Carbon Society of Japan