Formation process of CuCl2–NiCl2–graphite intercalation compounds

Abstract

The intercalation reaction of NiCl2 from the mixture of CuCl2 and NiCl2 has been studied by using natural graphite and a stage 1 graphite intercalation compound with CuCl2 at different temperatures from 400 °C to 550 °C for a wide range of residence times up to 8 days. In the mixture of CuCl2 and NiCl2, CuCl2 was found to be intercalated preferentially in the beginning of the reaction. At low reaction temperatures, NiCl2 was intercalated with the increase in heating time, but its content was saturated at a rather low value, NiCl2/C = 25 wt.% after 3 days at 450 °C, for example. At temperatures as high as 550 °C, however, the content of CuCl2, which had been intercalated in the beginning of the reaction, was found to decrease and NiCl2 started to be intercalated by prolonged heating, suggesting the exchange of the former with the latter. From the reactions of a stage 1 CuCl2–GIC with the mixture of CuCl2 and NiCl2, it was clearly revealed that the intercalated CuCl2 was replaced successively by NiCl2 in keeping the stage 1 structure. The saturated content of NiCl2 in respect to graphite depended strongly on the reaction temperature, attaining NiCl2/C = 150 wt.% at 550 °C. As seen by energy dispersive x-ray spectroscopy, NiCl2 intercalation proceeds from the periphery of the host particles. To form a uniform distribution of both intercalates, CuCl2 and NiCl2, it took a long time of residence, more than 3 days at 550 °C.