Investigations on Nb2C monolayer as promising anode material for Li or non-Li ion batteries from first-principles calculations

First-principles calculations are performed to study the electronic properties and metal ion storage capabilities of the two-dimensional (2D) Nb2C monolayer and its corresponding fluoride and hydroxide materials. We show that the Nb2C monolayer and the derived Nb2CF2 and Nb2C(OH)(2) are all metallic in their most stable configurations. We systematically investigate the adsorption and surface diffusion of different metal atom species A = Li, Na, K, Be, Mg, Ca, Al. We find that the bare Nb2C monolayer has excellent performance in the case of Li or Mg: the material remains metallic after adsorption; the ion diffusion is fast with extremely low diffusion barrier; the storage capacity is high (similar to 542 mA h g(-1) for Li and similar to 1084 mA h g(-1) for Mg); and the average intercalation potential is relatively low. Particularly, the diffusion barrier heights for the elements Li, Na, K, Mg and Ca are all lower than 0.1 eV. In addition, the functional groups tend to strongly degrade the performance, which should be avoided in experiment as much as possible. Our results suggest that the Nb2C monolayer is a promising anode material for Li- or non-Li-ion batteries.