Curvature induced improvement of Li storage in Ca2N nanotubes

Recently, Hu et al. reported that Ca2N monolayer is a good anode material for Na storage, but Li storage is not allowed since Li adsorption on Ca2N monolayer is energetically unfavorable. In this paper, from first-principles calculations, we predict that Li storage becomes possible when the Ca2N monolayer is rolling up into nanotubes. The curvature effect of the Ca2N nanotube decreases the Li adsorption energy to a level below 0 eV, corresponding to positive charge/discharge potential. As a result, Li storage in Ca2N nanotubes becomes feasible and a theoretical capacity of about 426.9 mAh/g is predicted for the Ca2N-(14, 0) nanotube. The metallic electronic structure and very fast Li/Na diffusion in the Ca2N nanotubes ensure that the rate performance of the Ca2N nanotubes can be good. This study offers an example of designing electrode materials for Li/Na ion batteries through curvature effect, and the strategy is applicable to other 2D materials.