Sodium into γ-Graphyne Multilayers: An Intercalation Compound for Anodes in Metal-Ion Batteries

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