Performance investigation of Ti x N x -1 O 2 MXene ( x = 2, 3, 4) as anode materials for Na-ion batteries by first-principles calculation.

The number of MXene layers plays a crucial role in their performance when they are used as anode materials for sodium-ion batteries. Herein, Ti-based nitride MXenes with different layers, Ti x N x -1 O 2 MXene ( x = 2, 3, 4) structures, were constructed to calculate the structural stability of their precursor, electronic properties after etching, and sodium storage behavior compared with the common Ti 2 CO 2 and Ti 3 C 2 O 2 MXene. First-principles calculations indicate that nitride MXenes possess a better rate capability than carbide MXenes of the same thickness. Moreover, the barrier for Na diffusion on the Ti 2 NO 2 MXene surface (0.114 eV) is lowest. Meanwhile, comparing the properties of three nitride MXenes with different thicknesses, Ti 2 NO 2 MXene performs relatively well with a high theoretical capacity with 756 mAh g -1 and a lower open circuit voltage of 1.1 V. In conclusion, the performance improvement of nitride MXene is not linear with thickness, because that of Ti 3 N 2 O 2 MXene is relatively weaker. This work lays the foundation for the feasibility of Ti 3 N 2 T x experimental preparation and provides corresponding evidence on the choice of MXene thickness. More attention should be paid to the etching method for Ti 2 NT x MXene.