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

Abstract

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°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.