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

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.

Spectroelectrochemistry of Carbon Nanotubes

“…Furthermore, supporting electrolytes like chlorides may trigger reactions with the SWCNT at anodic potentials. [27] The aprotic solvents were acetonitrile, [17,20,34, tetrahydrofuran, [25] DMSO, [9] ethylene carbonate/dimethylcarbonate [25] or ethylene carbonate/diethyl carbonate, [73] but the broadest electrochemical window is available in ionic liquids. [18] Polymer electrolytes, such as LiClO 4 + PEO (polyethylene oxide), [29,74,75] polyethyleneimine [76] or PC/PMMA (propylene carbonate/polymethylmethacrylate) [32,77,78] are useful for single nanotube studies.…”

“…[55] The G-mode in metallic tubes can be fitted by four components, allowing spectroelectrochemical studies of electron-plasmon coupling and Kohn anomaly. [55] The frequency of the G + -mode changes non-uniformly for n-doping, [14,17,19,25,63,73,84,[105][106][107][108] but monotonic blue shift occurs for p-doping. This shift was attributed to the CC bond contraction [Eq.…”

Double-walled carbon nanotubes: synthesis, structural characterization, and application

“…The Li + storage behaviors of highly pure DWCNT-derived buckypaper (consisting of entangled tube bundles) as an anode material in lithium ion batteries (LIBs) were studied using an in-situ the Raman technique [38]. The fabrication of DWCNT-derived buckypaper via a filtering process resulted in entangled long nanotube bundles of DWCNTs, wherein the nanotubes are packed into hexagonal arrays.…”

“…Low-frequency Raman spectra of the double walled carbon nanotubes during the discharge and charge processes. Reprinted from Kim et al [38] with permission from Wiley-VCH. http://carbonlett.org…”

Raman study on electrochemical lithium insertion into multiwalled carbon nanotubes

“…[9][10][11][12][13] It is demonstrated that both pristine and thermally treated thin tubes store Li + via both doping through defects on the outer surface as well as the formation of dilute intercalation compounds in the inter-shell spacing of the tubes.…”