Two-Dimensional VN MXene Monolayer as a High-Capacity Anode Material for Lithium-Ion Batteries and Beyond: First-Principles Calculations.

Two-dimensional metallic electrode materials with high energy density and excellent rate capability are crucial in rechargeable ion batteries. In this work, two-dimensional VN MXene monolayer has been predicted to be an attractive candidate anode material for rechargeable lithium, sodium, and magnesium ion batteries by first-principles calculations. We observe that VN monolayer is a metallic compound. The ion diffusion barriers on VN monolayer are predicted to be 0.025, 0.014, 0.004, and 0.058 eV for Li, Na, K, and Mg ions, respectively, which are rather low on the state-of-the-art two-dimensional energy storage materials. In addition, the calculated theoretical capacities of VN MXene monolayer are 925 mAh/g for Li ion, 463 mAh/g for Na ion, and 1850 mAh/g for Mg ion. The capacity of Li ions on VN monolayer is much higher than that of Li ions on the conventional anode graphite, and the extralarge capacity for Mg ions on VN monolayer is ascribed to the two-electron reaction and multilayer adsorption of Mg ions. Last, the average open circuit voltages of the VN MXene monolayer are also calculated to be 0.32 V for Li ions, 0.24 V for Na ions, and 0.34 V for Mg ions. These results provide a fundamental insight into electrochemical energy storage applications of two-dimensional VN MXene monolayer as a suitable candidate anode material for rechargeable Li, Na, and Mg ion batteries on the atomic scale.