A carbon hybrid material system consisting of single wall carbon nanotubes (SWCNTs) and fullerene (C 60 ) has been investigated using the first-principles methods. Through combining metallic SWCNTs with C 60 of high electron affinity, the lithium adsorption energy on this CNT-C 60 hybrid system (Γ2.110 eV) is found to be larger than that of the pure SWCNTs (Γ1.720 eV). By characterizing the electronic properties of the CNT-C 60 system such as band structure, density of states and charge distribution as a function of the Li adsorption in comparison with SWCNT or C 60 , it is also found that the Li adsorption takes place on the C 60 side preferably due to the large adsorption energy, which imparts metallic character to the C 60 in the CNT-C 60 hybrid system. Investigating various adsorption sites on the CNT-C 60 system in order to understand the adsorption mechanism of Li, it is found that Li atoms are preferably adsorbed at every other hexagonal or pentagonal site (next nearest neighboring sites) rather than every site (nearest neighboring sites) on the hybrid system.
The possibility of Li cluster formation in this CNT-C 60 system does not seem to be high since the Li-Li binding is less favorable than the Li adsorption on the CNT-C 60 system.