The effect of carbon starting material on carbon fluoride synthesized at room temperature - Characterization and electrochemistry

A series of carbon fluorine compounds (CxF) was prepared by catalyzed, room-temperature reactions of natural graphite, petroleum coke, and coal-tar-pitch coke with fluorine in the presence of HF and IF5. Elemental analysis indicated that most of the compounds had carbon-to-fluorine ratios between 1 and 2. X-ray diffraction, X-ray photoelectron spectroscopy, and infrared spectroscopy suggest that carbon-fluorine bond strengths were intermediate between ionic and covalent. The CxF materials exhibit higher reduction potentials when compared to commercially available CFx. Although the discharge capacities were lower for CxF compounds, their greater discharge voltage yielded higher energy densities than for analogous CFx cells. Discharge capacities for CxF increased slightly when prepared from petroleum coke heated to 1700 degreesC compared with coke heated to 2600 degreesC. This suggests that better discharge performance may be achieved from carbons with lower degrees of graphitization. CxF synthesized from natural graphite with particle sizes <10 m had a greater discharge capacity on a mass basis but a lower discharge efficiency based on F content when compared to CxF prepared from natural graphite with particle sizes between 20 and 40 mum. Materials prepared from coal-tar-pitch coke exhibited poor discharge capacities. (C) 2001 The Electrochemical Society. All rights reserved.