7Li NMR and ESR analysis of lithium storage in a high-capacity perylene-based disordered carbon

The lithium storage mechanism of perylene-based disordered carbon (PBDC) heat-treated at 550 degrees C, which is a promising material for use as the anode in lithium-ion cells, was studied by solid-state Li-7 NMR and ESR analysis. PBDC is one of carbonaceous materials containing condensed aromatic rings, and showed a high reversible specific capacity of about 800 mAh/g with large hysteresis in the charge/discharge profile. Li-7 NMR spectra for the lithiated PBDCs exhibited two bands at the insertion of above 900 mAh/g. Band A at 7 ppm and band B at 0.3 ppm versus LiCl were assigned to lithium in reversible and irreversible storage sites, respectively. The results of Li-7 NMR analysis supported the presence of ionic lithium located on aromatic rings. ESR spectra fbr PBDC lithiated by over 300 mAh/g showed sharp and broad signals. The intensity of the broad signal varied significantly with lithium insertion. The variations of Li-7 NMR and ESR spectra with lithium insertion were interpreted by the presence of two kinds of insertion sires; the layer structure site (L-site) and the unorganized carbon site (U-site) located between the L-sites. (C) 1997 Elsevier Science S.A.