Composites of (C4F)n and (CF)n Synthesized by Uncatalyzed Fluorination of Graphite

A new solid-state F-19 magic-angle spinning NMR signal at an isotropic F-19 chemical shift of -53 ppm is measured from graphite fluoride synthesized by reaction of graphite with F-2 at temperatures above 750 K with no catalyst. Two-dimensional NMR suggests the -53 ppm F-19 NMR signal originates from covalent fluoromethanetriyl groups belonging to ordered (CyF)(n) bulk domains composited with the major (CF)(n) domains. Quantitative F-19 and C-13 NMR find y = 4.32 +/- 0.64. DFT calculations of NMR chemical shifts for unsaturated fluorographene models show that a (C4F)(n) phase with fluorine bound covalently to a single side of the carbon layer best explains the observed NMR chemical shifts. We assign the new phase to this (C4F)(n) structure, which constitutes up to 15% of the carbon in our graphite fluoride composites. The (C4F)(n) content of the composite affects bulk electrochemical properties in a manner similar to graphite fluorides produced by conventional, catalyzed fluorination processes.