Theoretical investigations on single-walled carbon nanotubes (SWCNT) have been carried out using ab initio and molecular interaction potential with and without polarization (MIPp and MIP, respectively) methodologies to explore the possibilities of Li+ ion insertion through the side-wall of the nanotube. Li-nanotube systems can improve the capacity of lithium batteries by using both nanotube exteriors and interiors. Ab inito calculations of the fully optimized nanotubes were used to examine the topological defects depending on the ring size. The movement of the lithium cation through 8, 9 and 10-membered rings is studied and discussed.