NbN monolayer as a promising anode material for Li/Na/K/Ca-ion batteries: a DFT calculation.

Developing ranking anode materials with sufficient electrical conductivity, ultrafast ion diffusion ability and considerable storage capacity is of great importance for rechargeable ion batteries but still challenging. Herein, using first-principles calculations, the potential of monolayer Nb2N as an anode material for alkali metal (e.g., Li, Na, K and Ca) ion batteries (LIBs, SIBs, PIBs and CIBs) has been explored. The calculated results indicate that the Nb2N monolayer is dynamically and thermally stable with excellent electronic conductivity. To be specific, the Li, Na, K and Ca atoms can be steadily adsorbed on the Nb2N monolayer with a low adsorption energy of -0.996, -1.263, -1.568, and -1.401 eV, respectively. Impressively, the calculated low diffusion barriers for Li, Na, K and Ca on the Nb2N monolayer are 0.047, 0.029, 0.015 and 0.051 eV, respectively, implying its high performance for the ultrafast charge and discharge processes. More importantly, the maximum storage capacities are 536 mA h g-1 for LIBs and 1072 mA h g-1 for CIBs, which are much larger than those of common anode materials. This work not only demonstrates that the Nb2N monolayer can be used as a promising anode material but also inspires the future rational design of other nitride MXenes in energy conversion and storage devices.