Fluorine-graphite Intercalation Compounds Research Articles

Preparation, structure, and electrical conductivity of fluorine-graphite intercalation compound

Fluorine-graphite intercalation compound (GIC) has been prepared from pitch-based carbon fiber and powdery natural graphite in the presence of silver fluoride. Prepared compounds are stage 2: C 5–8F, stage 2 + 3: C 8–9F, stage 3: C 9–12F and stage 4: C 13–17F. The rate of fluorine intercalation in graphite is larger in the present system than in other metal fluorides examined previously. X-ray diffraction data indicate that C x F belongs to a hexagonal system with a superlattice of a 0 = 2 a g in the ab plane, accompanying some amount of a bi-intercalation phase. Lattice parameters of stage 3 C 10.9F were a 0 = 4.921 A ̊ , c 0 = 12.733 A ̊ , and those for stage 3 C 8.6F were a 0 = 4.918 A ̊ , c 0 = 12.817 A ̊ . The difference in lattice parameters arises from the increase in electron transfer from carbon to fluorine. The ideal composition of C x F is expressed as C 4 n F ( n = stage number). The highest electrical conductivity is given at stage 3, being 2.3 × 10 4 Scm −1, which is about eight times a pristine pitch fiber.

Preparation and electrical conductivity of fluorine-intercalated graphite fibers

Fluorine-graphite intercalation compounds were prepared in the presence of CuF 2, AgF or TiF 4, and their electrical conductivities and stability were examined. Since these metal fluorides are hygroscopic, starting materials were metal powders, which were fluorinated at 200°C in a nickel reactor and successively used for the experiments. After repeating the introduction of fluorine into the reactor and the evacuation 3 times using rotary and diffusion pumps, no absorption due to hydrogen fluoride was confirmed by IR spectrum in every run of experiment in order to avoid cointercalation of hydrogen fluoride and fluorine. When CuF 2 and AgF were used, fluorine was intercalated into graphite and a trace of metal fluoride was detected in GIC. Experimental results suggest that these metal fluorides act as catalysts to aid the intercalation of fluorine. AgF having a lower melting point than CuF 2 was more effective for fluorine- intercalation. On the other hand, highly volatile TiF 4 was cointercalated with fluorine at around 200°C. The electrical conductivity was increased with increasing intercalated fluorine and reached the maximum value at the 3rd stage. The maximum conductivities were 9, 8 and 6 times those of pristine vapor-grown, pitch-based and PAN-based carbon fibers, respectively. The stability of GIC was the reverse order.