First-Principles Calculations of TiB 4 and TiB 5 as Anodes with High Capacity for Na-Ion Batteries.

The electrochemical properties of TiB 4 and TiB 5 monolayers in Na-ion batteries (NIBs) were studied by using the first-principles calculation method based on density functional theory. The TiB 4 /TiB 5 monolayer showed excellent Na storage capacity, capable of adsorbing two layers of Na with theoretical capacities of 1176.77 and 1052.05 mA g -1 , respectively. The average operating voltages of the TiB 4 and TiB 5 monolayers are 0.073 and 0.042 eV, respectively, indicating that they can be used as anode materials for NIBs. More interestingly, the exposed B surface not only brings a high theoretical capacity but also provides a relatively small diffusion barrier of 0.16 (for TiB 4 ) and 0.33 eV (for TiB 5 ), enhancing their rate capability in NIBs.