  We systematically evaluate the prospects of a novel 2D nanomaterial,
phosphorene, as anode for Na-ion batteries. Using first-principles
calculations, we determine the Na adsorption energy, specific capacity and Na
diffusion barriers on monolayer phosphorene. We examine the main trends in
electronic structure and mechanical properties as a function of Na
concentration. We find favorable Na-phosphorene interaction with theoretical
capacity, exceeding those of alternative monolayer anodes for Na-ion batteries.
We find that Na-phosphorene undergoes semiconductor-metal transition at high Na
concentration. Our results show that Na diffusion on phosphorene is fast and
anisotropic with the energy barrier of only 0.04 eV. Owing to the high
capacity, good stability, excellent electrical conductivity and high Na
mobility, monolayer phosphorene is a very promising anode material for Na-ion
batteries. The calculated performance in terms of specific capacity and
diffusion barrier is compared to other layered 2D electrode materials, such as
graphene, MoS2, polysilane, etc.
