α-graphyne as a promising anode material for Na-ion batteries: a first-principles study

Abstract

Lithium-ion batteries (LIBs) have emerged as a technological game-changer. Due to the rising price of lithium and the environmental concerns LIBs pose, their use is no longer viable. Sodium (Na) may be the best contender among the alternatives for replacing lithium. Conventional graphite has a limited capacity for Na storage. Hence, α-graphyne, an allotrope of carbon, was studied here as a potential anode material for Na-ion batteries (NIBs), employing density functional theory. In-plane Na atom adsorption results in a semi-metallic to metallic transition of α-graphyne. Electronic transport calculations show an increase in current after Na adsorption in graphyne. The successive adsorption of Na atoms on the surface of graphyne leads to a theoretical capacity of 1395.89 mA h g−1, which is much greater than graphite. The average open circuit voltage is 0.81 V, which is an ideal operating voltage for NIBs. Intra- and inter-hexagon Na diffusions have very low energy barriers of 0.18 eV and 0.96 eV, respectively, which ensure smooth operation during charge/discharge cycles. According to this study, the α-graphyne monolayer thus has the potential to be employed as an anode in NIBs.