First-Principle Study of Black Phosphorus as Anode Material for Na Ion Batteries

Sodium-ion batteries are promising alternatives to lithium-ion batteries for large-scale applications. However, the low capacity, poor rate capability and high redox potential of existing anodes for sodium-ion batteries are bottlenecks for future developments. Black phosphorus has recently been found to be an excellent candidate for sodium-ion batteries anode material due to its high capacity and reasonable charge and discharge potentials. In this study, we investigated theoretical capacity and Na-ion diffusion barriers on black phosphorus using density functional theory (DFT) calculations. We found that Na diffusion on black phosphorus was fast and anisotropic with energy barrier of only ~ 0.2eV along [100] direction. Moreover, Na-ion diffusion in a specific direction could be enhanced by applying mechanical strain. Furthermore, we examined the effect of surface and edge sites on the Na-ion transport properties of black phosphorus. Owing to the high capacity, good conductivity and excellent Na mobility, black phosphorus is expected to be a very promising anode material in Sodium-ion batteries