Anatase TiO2 nanotubes as Li-ion battery anodes: A molecular dynamics study of Li-ion adsorption on anatase nanotubes

Lithium ion batteries are widely used in many electronic devices to store energy and release it when needed. Higher storage capacities and higher charge/discharge rates necessitates use of advanced materials. One way of increasing this rate is surface storage rather than bulk storage of Li-ions. This is facilitated by nanosizing the electrodes. One of the potential candidates for this task as the Li-ion battery anode is TiO2 nanotubes. In this research we studied the adsorption of Li-ions on anatase nanotubes using molecular dynamics simulations. Li-ions are dispersed in a simulation box around a TiO2 nanotube and due to the non-bonding interactions, they adsorb on the nanotubes. Our results showed that the volume change of the nanotubes due to this adsorption is negligible which enhances the cycle life of these anodes. And with increasing the temperature to 1000 K, the number of adsorbed ions increases and remains close to the maximum, but With further increase in temperature, the number of adsorbed ions decreases over time. We have also confirmed that the Li-ions adsorb in tetrahedral sites of anatase and molecular dynamics simulations in the range of nanoseconds cannot capture the hopping of these ions within the tetrahedral sites. In addition, using the adsorption isotherms we showed that when the surface coverage is small the adsorptions obey a Langmuir-type isotherm.