We investigated the effect of the curvature in lithium storage at single-walled carbon nanotubes, with both ab-initio and Molecular Dynamics simulations. Our results show that the carbon rings of nanotubes develop strong cation-pi- interactions with Li ion. These interactions result in positioning the alkali metal cation on top of a phenyl group. By using different types of carbon nanotubes it was revealed that the interaction is not affected by the type or the curvature of the nanotubes. Molecular Dynamics simulations of lithium intercalated nanotube bundles pointed at the fact that the cations remain attached to the nanotubes even at room temperature, with a maximum Li to C ratio of 1:2.1.