α-Graphyne nanotubes as a promising material for Li-ion battery anodes

Developing high storage capacity of lithium-ion batteries (LIBs) by applying novel anodes based on nanostructures has been allocated to extensive research. Although, SP2-hybrid carbon nanostructures exhibit a low storage capacity, a two-dimensional (2D) graphyne (Gy) monolayer is proved to be an efficient electrode material due to its large surface area and significant mechanical and chemical properties. Herein, a derivative of Gy called alpha-graphyne nanotube (alpha GyNT) is proposed as the anode material of LIBs, in which the adsorption of lithium (Li) on Gy nanobelt (GyNB) (one-segment) and short open-ended GyNTs with different lengths are modeled by implementing of ab initio first-principles calculations. Lithium diffusion behaviors inside and outside of GyNTs has been investigated by ab initio molecular dynamics (ABMD) to calculate open-circuit voltage. The results reveal that Li adsorption energies of short alpha GyNTs have no regular oscillatory dependence on the number of segments along the tube axis (length of the tubes). Furthermore, the largest storage capacity of C4Li4 (1273.75 mAh/g) was obtained for (4, 4) alpha GyNTs, which demonstrate better storage capacity compared to single/multiple graphyne nanostructures. The curvature of alpha GyNTs can enhance the diffusion of Li atoms and leads to promote storage capacities, which suggest these anode materials improve LIBs's performance.