Curvature induced improvement of Li storage in Ca2N nanotubes

Highlights: • Curvature effect enhances Li/Na adsorption on the inner surface of the Ca₂N-nanotubes. • Li storage in Ca₂N-nanotubes becomes possible due to the curvature effect. • The theoretical capacity of 2D anode materials can be tailored through curvature effect. • Curvature do not change the good rate performance of the Ca₂N materials. 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.