Sodium\ninto γ‑Graphyne Multilayers: An\nIntercalation Compound for Anodes in Metal-Ion Batteries

The bulk synthesis of γ-graphyne has been recently\nachieved\nand evidenced a multilayered structure, which suggests its potential\nexploitation as a substitute of graphite-based anode materials for\nmetals heavier than lithium (Li). In fact, each of its regular pores\nof sub-nanometric size features an optimal environment for hosting\na single sodium (Na) ion, as reported here by means of accurate electronic\nstructure calculations. We show that the graphyne<i>/</i>Na ion coupling mimics that found on the graphene<i>/</i>Li ion in terms of metal-single layer interaction and equilibrium\ndistance. More importantly, in contrast to what is found for graphite,\nwe demonstrate that graphyne intercalation compounds with Na are thermodynamically\nstable and feature an optimal storage capacity of 372 mAh·g<sup>–1</sup>. These findings, together with a limited crystal\nstructure expansion upon Na intercalation, a low metal diffusion barrier\nas well as high electrical conductivity, pave the way to the development\nof novel graphyne-based anodes for efficient Na-ion batteries.