In situ Raman study on single- and double-walled carbon nanotubes as a function of lithium insertion.
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.
Kim
Yoong Ahm
YA
Department of Electrical and Electronic Engineering, Faculty of Engineering, Shinshu University, Nagano 380-8553, Japan. yak@endomoribu.shinshu-u.ac.jp
Kojima
Masahito
M
Muramatsu
Hiroyuki
H
Umemoto
Souichiro
S
Watanabe
Takaaki
T
Yoshida
Kazuto
K
Sato
Keigo
K
Ikeda
Takuya
T
Hayashi
Takuya
T
Endo
Morinobu
M
Terrones
Mauricio
M
Dresselhaus
Mildred S
MS
D004563:Electrochemistry / Q000379:methods*; D004574:Electromagnetic Fields; D008094:Lithium / Q000737:chemistry* / Q000528:radiation effects; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000528:radiation effects / Q000648:ultrastructure; D036103:Nanotechnology / Q000379:methods*; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000528:radiation effects; D010316:Particle Size; D013059:Spectrum Analysis, Raman / Q000379:methods*
D037742:Nanotubes, Carbon; D008094:Lithium