Long-term stability of fluorine–graphite intercalation compound prepared under high pressure of fluorine

Fluorine–graphite intercalation compounds were prepared from highly oriented pyrolytic graphite (HOPG) and natural graphite under high pressure of fluorine (16 MPa) at room temperature and were analyzed by means of X-ray diffraction. The rate of intercalation under high pressure of fluorine was higher than that under ordinary pressure. The compositions of the compounds obtained from HOPG and natural graphite were estimated by the weight change before and after fluorination to be C3.41F and C5.62F, respectively. They were blue–black compounds composed of two different phases. One phase is a conventional stage II CxF with the repeat distance of ca. 0.93–0.96 nm which was the same compound as that obtained under ordinary pressure of fluorine, and the other was also a stage II with a different repeat distance of ca. 1.03–1.18 nm. The fluorine species intercalated between the graphene layers can easily move between both phases and the phase transition occurs periodically. The decomposition rate of fluorine-intercalated HOPG was extremely low and it shows a long-term stability in air for 26 years.