Novel two-dimensional tetragonal vanadium carbides and nitrides as promising materials for Li-ion batteries

Two-dimensional (2D) materials, owing to their unique properties, have shown great potential for energy storage. In this work, we predict two types of new 2D transition metal carbides and nitrides, namely, tetragonal V₂C₂ and V₂N₂ (tetr-V₂C₂ and tetr-V₂N₂) monolayer sheets. Comprehensive first-principle calculations show that these two 2D systems exhibit dynamic (thermal) stabilities and intrinsic metallic nature. Compared with the commercialized graphite anode material, tetr-V₂C₂ and tetr-V₂N₂ monolayer sheets exhibit lower Li diffusion barrier of 89 and 94 meV, higher theoretical capacity of 412 and 425 mA h g^-1 and lower average open circuit of 0.468 and 0.583 V, respectively. Combining those advanced features, our proposed tetr-V₂C₂ and tetr-V₂N₂ monolayer sheets are both promising candidates as anode materials for lithium-ion batteries (LIBs) in the future.