Is borophene a suitable anode material for sodium ion battery?

2D Boron is an atomically thin layer of boron with both light weight and metallicity, two kinds of potential structures are proposed, namely, a close-packed triangular B layer(denoted B△ hereafter) and a hexagonal voids or vacancies ( ) in B layer(denoted hereafter) (Evgeni S. et al. Nano Lett. 2012, 12, 2441–2445). Here, we use first-principles calculations to investigate the potential of borophene as an anode material for sodium-ion batteries. It is found that borophene has an adsorption energy to sodium atoms of −1.448 eV for all boron atoms in the plane ( ) and −1.731 eV for BΔ. The fully sodiated phase of borophene is Na0.083B and Na0.1B for BΔ and , respectively, which corresponds to a theoretical specific capacity of 248 mAh g−1 (496 mAh g−1 for two sides) for BΔ and 298 mAh g−1 (596 mAh g−1 for two sides) for . The energy barrier along the furrow of corrugated borophene is only 12 meV for BΔ, which suggests that sodium diffusion on borophene can be extremely fast for BΔ. In addition, a strong directional anisotropy is observed for sodium diffusion with a 352.5 meV barrier perpendicular to the furrow of BΔ. Finally, both exhibit metallic characteristics during the entire sodiation process, which indicates that the material has excellent electronic conductivity. The findings in this work suggest that as an anode material for sodium-ion batteries, borophene can drastically boost the energy and power density of batteries.