Theoretical investigations on boron and nitrogen-doped single-walled carbon nanotubes have been carried out using ab initio calculations to explore the capability of the nanotubes to incorporate Li⁺ ion in its interior. Li-nanotube systems can improve the capacity of lithium batteries by using both nanotube exteriors and interiors. Ab initio calculations of the fully optimized nanotubes and their complexes with lithium were used to examine the lithium incorporation in the nanotube through the open-end depending on the doping. The energetic and geometric features of the complexes are studied and discussed.