The intercalation and diffusion of lithium ions in a bundle of carbon nanotubes were investigated via an ab initio molecular dynamics simulation method based upon the density functional theory. It was found that lithium ions quickly penetrate into the carbon nanotubes and the space between neighboring carbon nanotubes. With a low Li ion density, the Li ions tend to stay close to the nanotube ends. Interestingly, Li ions were able to penetrate through the carbon nanotube and move from one end to the other. It was also discovered that Li ions could remain between two neighboring carbon nanotubes, which presents a new approach for Li ion intercalation and storage. Importantly, Li ions located among three neighboring carbon nanotubes have very strong adsorption potentials that were a factor of four larger than those of Li ions located along the central axis of a single-walled nanotube. This indicates that Li ions located among three neighboring carbon nanotubes would be very difficult to remove from a nanotube bundle, which suggested that Li storage capacity in this case was possibly irreversible, and that keeping the nanotubes apart with an appropriate distance would hinder or promote the formation of irreversible intercalation.

Intercalation and Diffusion of Lithium Ions in a Carbon Nanotube Bundle by ab initio Molecular Dynamics Simulations. Song, B., Yang, J., Zhao, J., Fang, H.: Energy and Environmental Science, 2011, 4[4], 1379-84