Electrochemical Li Insertion in B-Doped Multiwall Carbon Nanotubes

Abstract

Electrochemical Li insertion into boron-doped multiwall carbon nanotubes (B-MWNTs) was investigated in a nonaqueous medium. Transmission electron microscopy observations showed that the walls of the tubes consisted of highly aligned ca. 35-45 graphene layers with good 3D ordering feature. Raman studies revealed that boron doping in multiwall carbon nanotubes (MWNTs) destroyed the local hexagonal symmetry. X-ray photoelectron spectra of B-MWNTs further supported the results of Raman spectra and confirmed the presence of BC3BC3 nanodomains. N2N2 adsorption measurements indicated that the Brunauer-Emmett-Teller (BET) surface areas of undoped and doped nanotubes were 10 and 12 cm²/g, respectively, with almost similar mesopore volumes. Galvanostatic discharge-charge measurements revealed that the reversible capacity was 156 mAh/g for undoped and 180 mAh/g for B-doped nanotubes in the first cycle with almost equal coulomb efficiencies of 55-58%. The coulomb efficiency increased to more than 90% after the second cycle. Cyclic voltammetry (CV) showed that highly reversible intercalation/deintercalation of Li occurred with some undesirable reduction processes in the initial discharge process. The cycle lives of both undoped and doped samples were quite satisfactory. Slow-scan CV confirmed that the intercalation of lithium in these nanotubes occurred through staging transition, usually observed in Li graphite intercalation compounds. © 2001 The Electrochemical Society. All rights reserved.