Theoretical investigations have been carried out to explore the possibiliti
es of Li+ ion intercalation or insertion through the side-wall or through t
he cap region of carbon nanotubes. Hartree-Fock(HF), MP2 and density functi
onal (DFT) theories with minimal to extended basis sets were used to examin
e simple models of 5, 6, 7, and eight-membered-rings. The barrier to insert
Li+ ion through these rings depends on the ring size. Insertion is easier
as the ring size increases. Lithium ion favors two positions: (a) inside th
e tube close to the wall, and (b) outside of the tube. Energetic informatio
n is provided using simple models with different diameters. Movement of the
cation(s) within a single-wall tube, in interstitial zone and within multi
wall tube, are also studied and discussed.