Electrochemical behaviors of carbon alloy BCx and of BCx-coated graphite prepared by chemical vapor deposition

Boron-substituted carbons (C/B = 3.8-18.8) have been synthesized by chemical vapor deposition (CVD) using benzene, boron trichloride and hydrogen at 800-1000 degrees C in the presence of a nickel catalyst under atmospheric pressure. BCx prepared with the nickel catalyst had a higher crystallinity than that prepared in the absence of nickel. BCx samples prepared by short duration deposition showed relatively higher charge capacities and better cycleability due to a smaller amount of the less organized region. A longer duration of the reaction,; however, yielded a larger amount of less crystallized regions within BCx. BCx compounds have also been coated by CVD using cyclohexane as a carbon source on two kinds of graphite: natural graphite powder and graphite treated with 94% HNO3. XPS and Raman spectroscopy indicated that these materials were not mixtures of BCx and graphite, but BCx-coated graphites. The BCx-coating modified the charge-discharge profiles of natural graphite. The potential of the electrode was low and flat and gradually increased during the last stage of lithium ion deintercalation reaction. (C) 1999 Elsevier Science Ltd. All rights reserved.