LI-7 NMR AND ESR ANALYSIS OF LITHIUM STORAGE IN A HIGH-CAPACITY PERYLENE-BASED DISORDERED CARBON

The lithium storage mechanism of perylene-based disordered carbon (PBD C) heat-treated at 550 degrees C, which is a promising material for us e as the anode in lithium-ion cells, was studied by solid-state Li-7 N MR and ESR analysis. PBDC is one of carbonaceous materials containing condensed aromatic rings, and showed a high reversible specific capaci ty of about 800 mAh/g with large hysteresis in the charge/discharge pr ofile. 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 p pm versus LiCl were assigned to lithium in reversible and irreversible storage sites, respectively. The results of Li-7 NMR analysis support ed the presence of ionic lithium located on aromatic rings. ESR spectr a fbr PBDC lithiated by over 300 mAh/g showed sharp and broad signals. The intensity of the broad signal varied significantly with lithium i nsertion. The variations of Li-7 NMR and ESR spectra with lithium inse rtion 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.