2D-VN2 MXene as a novel anode material for Li, Na and K ion batteries: Insights from the first-principles calculations.

Developing two-dimensional (2D) materials as anode materials have been proved a promising approach to significantly improve the charge storage performances of alkali metal ion. Herein, we investigate mono-layered VN2 as an anode material in Li, Na and K ion batteries. Firstly, the high stability of 2D-VN2 has been demonstrated via calculating the phonon spectra. 2D-VN2 is capable of delivering high capacities of 678.8, 339.4 and 1357.6 mAh g-1 in Li+, K+ and Na+ storage, respectively. In addition, the metallic properties and corresponding high electrical conductivity and low diffusion barriers of 201.1 meV for Li atoms, 34.7 meV for K atoms and 84.1 meV for Na atoms on VN2 surface, indicating good capacity and the superior rate performances of alkali metal atoms migration on VN2. The calculated average voltage of Li, Na and K are respectively 0.81 V, 0.29 V and 0.77 V, suggesting a promising voltage behavior compared with other 2D materials.