Electrochemical storage of lithium in multiwalled carbon nanotubes

Abstract

Multiwalled carbon nanotubes (MWNT) have been obtained by catalytic decomposition of acetylene at 900°C over silica supported cobalt. The thermal treatment at 1600, 2000 and 2800°C allowed improvement of their structural and microtextural organization as well as the elimination of any remaining nanoparticles of cobalt. Such a tubular carbon host with graded texture and chemical composition is a very convenient material for studying the electrode processes during insertion and extraction of lithium in an aprotic medium. The specific capacity, that is, the degree of irreversible (500–100mAhg−1) and reversible (400–100mAhg−1) insertion of lithium, has been estimated from galvanostatic charge–discharge characteristics. The voltage profiles supplied information about the main redox reactions, electrolyte decomposition and capacitance effects. Especially, the high divergence in some cases between the values of potentials for insertion and extraction of lithium, so called hysteresis, was carefully considered. The analysis of texture, porosity, surface area, chemical composition, kind of heteroatoms and type of their bonding with carbon allowed better elucidating the mechanism of lithium insertion. Complementary techniques, that is, elemental analysis, X-ray photoelectron spectroscopy experiments, gas adsorption, transmission electron microscopy, galvanostatic and potentiodynamic investigations were used for the full structural characterization of the carbon nanotubes and the electrochemical storage of lithium.