Determining factors for the intercalation into carbon materials from organic solutions

Abstract

Based on our experimental results reported previously, the factors determining the spontaneous intercalation reactions of alkali metals and iron chloride in organic solutions at room temperature were discussed for pyrolytic carbons and cokes with different heat treatment temperature. Three cases occurred; the formation of ternary intercalation compounds, i.e., intercalation of solvated intercalates, that of binary compounds by the intercalation of non-solvated ions, and no intercalation at all. These experimental results was discussed from the competition among three factors; (1) resistance to expansion of the gallery of carbon layers in host carbons, (2) electrostatic interaction between host carbons and intercalates, either solvated or non-solvated, and (3) strength of solvation with intercalate ions. In cases of Li and K in THF, ternary compounds were obtained from most cokes, which may be explained as follows; the electrostatic interaction between their voluminous solvated cations and cokes with different crystallinity (factor 2) always overcame the resistance to expansion of the gallery (factor 1). In the case of Na, however, binary compounds with high stage structures were obtained from most coke hosts because electrostatic interaction with non-solvated Na ions (factor 2) could not overcome the resistance to expansion (factor 1), but that with non-solvated Na ions could. Into pyrolytic carbons, solvated alkali metal ions, including Na, could be intercalated, irrespective of heat treatment temperature, probably because of easy expansion due to intercalation in one direction of the sample plates. In the case of an acceptor type FeCl 3, its concentration in nitromethane solution had to be high enough (factor 2) to overcome the resistance to expansion (factor 1) of the cokes heat-treated at low temperatures, though pyrolytic carbons can be intercalated by FeCl 3 from solutions even with its low concentration.