Intercalation of lithium into natural graphite flakes and heat-treated polyimide films in ether-type solvents by chemical method

Abstract

X-ray diffraction and Raman spectroscopy have been used to study the intercalation of Li into natural graphite flakes and heat-treated polyimide films (HTT = 1800–3000 °C) by chemical method in various ether-type solvents. Here, naphthalene was used as a dissolving agent for Li, and the solvents were tetrahydrofuran (THF), 2-methyltetrahydrofuran (MeTHF), 2,5-dimethyltetrahydrofuran (diMeTHF), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), 1-methoxypropane (MP), 1-methoxybutane (MB) and diethyl ether (Et 2O). First, to elucidate the effects of the solvents, natural graphite flakes were used as a host material. By use of THF, DME and DEE, co-intercalation of Li and these solvents occurred to form ternary Li—solvent graphite intercalation compounds (GICs), but binary Li-GICs without solvents were obtained in MeTHF, diMeTHF, MP, MB and Et 2O solvents. These results were confirmed by (00 l) X-ray diffraction patterns. Second, co-intercalation of Li and THF into the heat-treated polyimide films was studied mainly by use of the Raman scattering results. As a result, co-intercalation of Li and THF occurred to form Li—THF—GIC for highly graphitized polyimide films heat-treated above 2400 °C, while only Li was found to be intercalated into the less graphitized films heat-treated below 2100 °C.