Masayuki Oguchi

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

Abstract The lithium storage mechanism of perylene-based disordered carbon (PBDC) heat-treated at 550 °C, which is a promising material for use as the anode in lithium-ion cells, was studied by solid-state 7 Li 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. 7 Li 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 7 Li NMR analysis supported the presence of ionic lithium located on aromatic rings. ESR spectra for 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 7 Li NMR and ESR spectra with lithium insertion were interpreted by the presence of two kinds of insertion sites: the layer structure site (L-site) and the unorganized carbon site (U-site) located between the L-sites.

Study of Molecular Structures and Properties of Europium(III) Complexes with Phosphine Oxides by NMR Analysis

The 31P-NMR spectra of europium complexes with β-diketones and phosphine oxides in CDCl3, DMSO-d6, toluene-d8 with dissolved fluorinated polymers, and fluorinated solvent were investigated as well as the temperature dependence of these spectra. When a mixture of europium complex 1 and 1.0 molar equivalent of trioctylphosphine oxide and triphenylphosphine oxide was dissolved in a fluorinated solvent, europium complex 2 with two types of phosphine oxides was formed at room temperature. In CDCl3 and toluene-d8 solutions, however, this complex was identified only at low temperatures. This difference is thought to be due to the differences in the speed of ligand exchanges. In DMSO-d6 solution, no signal corresponding to the europium complex with phosphine oxides was observed. This implies that the major portion of phosphine oxides is not coordinated with europium ions in DMSO-d6 solution. The fluorescence intensity of each europium complex in a solvent was correlated to the solvent and the 31P-NMR spectrum. It was found that the fluorescence intensity was the highest in the fluorinated solvent.