Role of strain and concentration on the Li adsorption and diffusion properties on Ti₂C layer

The performance of Li-ion batteries relies heavily on the capacity and stability of constituent electrodes. Recently synthesized 2D MXenes have demonstrated excellent Li-ion capacity with extremely high charging rates. In this work, first-principles calculations are employed to investigate the effects of external strain and Li concentration on the adsorption and diffusion of Li on Ti₂C layer, a representative MXene. Our calculations demonstrate that the binding energy of Li atoms decreases monotonically with external strains, and the mechanical properties are not influenced by Li adsorption. For multiple Li atoms adsorption, their stable configurations show that the Li atoms tend to reside in one side first, in contrast with other 2D materials. We further show that the binding energy of Li is weakly dependent on the Li concentration. The diffusion barrier is calculated, and the results show that the strain and concentration have limited effects on the diffusion of Li atoms. Finally, the adsorption of Li atoms on two types of Ti₂C double layer are considered. For all studied structures, their stabilities are examined by molecular dynamics simulations carried out at room temperature. The influence of Li adsorption on the electronic structures of Ti₂C layer is also discussed. Our results suggest that Ti₂C could be a promising electrode material for lithium ion batteries in terms of lithium storage capacity and stability at a high Li recycling rate. © 2014 American Chemical Society.