Theoretical study of alkali atom doped outside 4 angstroms carbon nanotubes

Using first-principles calculations, we study the doping of alkali atoms on the outer surface of 4 angstroms single-walled carbon nanotubes. It is found that the exterior doping at the "center" site is more favorable than the interior doping along tube axis. The calculated binding energies show a strong chirality dependence, and the alkali atoms tend to be bound strongest with the (5, 0) tube. The change of band structure upon doping is studied and the charge transfer between tube and alkali atom is shown. Our calculations indicate that the Li storage capacity can be reached to a maximum of LiC2.5, which suggests that the 4 angstroms nanotube could be a plausible candidate for Li-ion battery applications.