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Carbon nanotubes were investigated by means of electron energy-loss spectroscopy. Two peaks due to the π plasmon and the π+σ plasmon were observed. The energy of the π+σ plasmon peaks varied from 22.0 eV to 24.5 eV, which roughly agrees with the average plasmon energy of graphite. A shoulder due to single electron excitations was observed at 13 eV, which was not observed in graphite. There were two kinds of nanotubes which exhibited their respective π plasmon peaks at 5.2 eV and 6.4 eV. The peaks in the dielectric function obtained by Kramers-Kronig analysis of the spectra were broader than those of graphite probably due to the curving of the graphitic sheets.

We conducted a long-term cycling test of a commercial 18650-type lithium-ion battery with a capacity of 3100 mA • h at room temperature and investigated the degradation mechanism of the battery's LiNi 0.82 Co 0.15 Al 0.03 O 2 positive electrode. Sphericalaberration-corrected scanning transmission electron microscopy (Cs-STEM) revealed the presence of a thick degraded surface layer on the surface of the positive active material after the cycling test, and electron energy loss spectroscopy (EELS) revealed that the degraded surface layer continuously evolved from a LiNiO 2 layered structure to a NiO structure, in the direction from the bulk toward the surface. Hard X-ray photoemission spectroscopy (HX-PES) indicated that the majority of low-valence Ni existed on the surface of the positive active material, which was charged after the cycling test, and that the degraded surface layer was inactive against charge reaction. The results suggest that the degraded surface layer was responsible for battery degradation during the cycling test. X-ray photoemission spectroscopy (XPS) indicated that Li 2 CO 3 increased on the surface of the positive electrode after the cycling test. The phenomena would contribute to the formation of the degraded surface layer on the surface of the positive active material.

Transmission electron energy-loss spectra of single-shell carbon nanotubes were measured and compared with those of multishell carbon nanotubes and graphite. Two peaks due to the π plasmon and the π+σ plasmon were observed at 5.8 eV and 20.6 eV, respectively. The energy of the π plasmon takes a value between those of two kinds of multishell tubes. The energy of the π+σ plasmon is lower than those of multishell tubes and graphite by 2 eV and 6 eV, respectively. The 1s→π* and 1s→σ* transition peaks of the single-shell tubes are much broader than those of the multishell tubes and graphite. The reason for the broadening may be due to the strong curving of the graphitic sheets.

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