Facile diffusion of lithium ions in carbon nanotubes is crucial for their development as anode materials of Li ion batteries. All-electron density functional theory computations show that very high energy barriers have to be overcome when Li penetration from exohedral to endohedral sites through the perfect sidewalls of pure C and composite BC3 nanotubes. However, these barriers are reduced substantially when topological defects (seven-, eight-, and especially nine-membered rings) are present, and the effect for composite BC3 nanotubes is more significant. This suggests efficient approaches to achieve higher diffusion rates and greater Li storage capacity in nanotube-based lithium ion batteries. (c) 2005 Elsevier B.V. All rights reserved.