Ab initio prediction of borophene as an extraordinary anode material exhibiting ultrafast directional sodium diffusion for sodium-based batteries

Density functional theory calculations and ab initio molecular dynamics simulations are performed to study the feasibility of using borophene, a newly synthesized two-dimensional sheet of boron, as an anode material for sodium-ion and sodium-oxygen batteries. The theoretical capacity of borophene is found to be as high as 1,218 mAh g(-1) (Na0.5B). More importantly, it is demonstrated that the sodium diffusion energy barrier along the valley direction is as low as 0.0019 eV, which corresponds to a diffusivity of more than a thousand times higher than that of conventional anode materials such as Na2Ti3O7 and Na3Sb. Hence, the use of borophene will revolutionize the rate capability of sodium-based batteries. Moreover, it is predicted that, during the sodiation process, the average open-circuit voltage is 0.53 V, which can effectively suppress the formation of dendrites while maximizing the energy density. The metallic feature and structural integrity of borophene can be well preserved at different sodium concentrations, demonstrating good electronic conductivity and stable cyclability.