Two-dimensional AlB 4 /Al 2 B 2 : high-performance Dirac anode materials for sodium-ion batteries.

Sodium-ion batteries (SIBs) have attracted much attention due to their abundant earth-reserves and low cost. Two-dimensional (2D) Dirac materials show great application prospects as anodes for SIBs because of their excellent electronic conductivity. We explore the performances of AlB 4 (Al 2 B 2 ) monolayers and bilayers as anodes for SIBs by using first-principles calculations. The AlB 4 (Al 2 B 2 ) monolayer exhibits a high theoretical storage capacity of 954.15 (709.17) mA h g -1 and a low diffusion barrier of 0.36 (0.03) eV. The calculated average open-circuit voltage (0.68/0.18 V) falls within the acceptance range of 0.1-1.0 V for anode materials. The fully sodiated AlB 4 (Al 2 B 2 ) monolayer shows a tiny lattice expansion of 0.9% (2.4%), suggesting good reversibility. Furthermore, in comparison with the AlB 4 (Al 2 B 2 ) monolayer, the AlB 4 (Al 2 B 2 ) bilayer can provide stronger binding with Na on the outside surface. These results contribute to a better understanding of the AlB 4 (Al 2 B 2 ) monolayers and bilayers as potential high-performance anode materials for SIBs.