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In Situ Raman Study on Single‐ and Double‐Walled Carbon Nanotubes as a Function of Lithium Insertion

2006; Wiley; Volume: 2; Issue: 5 Linguagem: Inglês

10.1002/smll.200500496

1613-6829

Yoong Ahm Kim, Masahito Kojima, Hiroyuki Muramatsu, Souichiro Umemoto, Takaaki Watanabe, Kazuto Yoshida, Keigo Sato, Takuya Ikeda, Takuya Hayashi, Morinobu Endo, Mauricio Terrones, M. S. Dresselhaus,

Graphene research and applications

Abstract We investigated the electrochemical lithium ion (Li + ) insertion/desertion behavior on highly pure and bundled single‐ and double‐walled carbon nanotubes (SWNTs and DWNTs) using an in situ Raman technique. In general, two storage sites could host Li + in SWNT and DWNT bundles when varying an external potential: a) the outer surface sites, and b) the interstitial spaces within the bundles. The most sensitive changes in the tangential mode (TM) of the Raman spectra upon doping with Li + can be divided into two regions. The first region was found from 2.8 to 1.0 V (the coverage of Li + on the outer surface of a bundled nanotube) and was characterized by the loss of resonant conditions via partial charge transfer, where the G + line of the SWNT and the TM of the outer tube of DWNTs experienced a highly depressed intensity, but remained almost constant in frequency. The appearance of a Breit–Wigner–Fano (BWF) profile provided strong evidence of metallic inner tubes within DWNTs. The second region was observed when the applied potentials ranged from 0.9 to 0 V and was characterized by Li + diffusion into the interstitial sites of the bundled nanotube material. This phenomenon invoked a large downshift of the G − band in SWNTs, and a small downshift of the TM of the inner tube of DWNTs caused by expansion of the CC bonds due to the charge transferred to the nanotubes, and the disappearance of the BWF profile through the screening effect of the interstitial Li + layers.