Investigation of Boron-Doped Graphdiyne as a Promising Anode Material for Sodium-Ion Batteries: A Computational Study.

In this work, by density functional theory (DFT) calculations, sp-sp-hybridized boron-doped graphdiyne (BGDY) nanosheets have been investigated as an anode material for sodium storage. The density of states (DOS) and band structure plots show that substituting a boron atom with a carbon atom in an 18-atom unit cell converts the semiconductor pristine graphdiyne (GDY) to metallic BGDY. Also, our calculations indicate that, due to the presence of boron atoms, the adsorption energy of BGDY is more than that of GDY. The diffusion energy barrier calculations show that the boron atom in BGDY creates a more suitable path with a low energy barrier for sodium movement. This parameter is important in the rate of charge/discharge process. On the other hand, the projected density of states (PDOS) plots show that sodium is ionized when adsorbed on the electrode surface and so Na-BGDY interaction has an electrostatic character. This type of interaction is necessary for the reversibility of adsorption in the discharge mechanism. Finally, the calculation of the theoretical capacity shows an increase in BGDY (872.68 mAh g) in comparison with that in GDY (744 mAh g). Thus, from comparison of different evaluated parameters, it can be concluded that BGDY is a suitable anode material for sodium-ion batteries.