Biphenylene Nanotube: A Promising Anode Material for Sodium-Ion Batteries

The properties of pristine and boron-doped biphenylene nanotubes (BPNT and BBPNT, respectively) as anode materials for sodium storage are studied using density functional theory (DFT). To this end, the electronic properties, adsorption energy, diffusion energy barrier, open-circuit voltage (OCV), and theoretical capacity are evaluated. The density of states calculations indicate that BPNT and BBPNT with zero band gap have a metallic character, which is critical for electron transferring in electrode materials. The calculation of adsorption energies suggests that the inside of the tube has better adsorption than the outside. Also, doping with boron improves the adsorption inside and outside the nanotube. Sodium ion sees three ways to penetrate from the outside to the inside of the tube. Calculations illustrate that the bigger ring with eight atoms with a 7.08 eV energy barrier, compared to the other cavities, is more appropriate for diffusion. This energy decreases to 5.84 eV after boron doping. The OCV profile of BBPNT confirms that this structure is in the acceptable voltage range for sodium-ion batteries (SIBs). Finally, this work obtains a theoretical capacity of 403.82 mAh g(-1) (without sodium clustering) for BBPNT, which confirms the potential of this structure for use in SIBs.