Graphene/Phosphorene nano-heterostructure as a potential anode material for (K/Na)-ion batteries: Insights from DFT and AIMD

Rechargeable Potassium and Sodium-ion batteries started to receive a vast amount of attention in recent years against their Lithium-ion counterparts. However, the development of a high-performing anode material for these ion batteries is still to be explored. In this work, we conduct a first-principles study on the adsorption and diffusion behaviors of Potassium (K) and Sodium (Na) in a Graphene/Phosphorene (G/P) van der Waals nano-heterostructure, in order to assess its suitability as an anode for both K-ion and Na-ion batteries. We investigate the electrochemical properties of the system, including binding energies, band structure, ion diffusivity out-side and in-side the G/P system, as well as the heterostructure's stability at a high metallic coverage. The calculated binding energies for K and Na are −2.69 eV and −2.42 eV, respectively, which are strong enough to prevent metallic clustering during the cycling. The diffusion of K/Na within G/P's regions shows strong directional anisotropy with a low diffusion barrier of 0.04 eV for K and 0.05 eV for Na along the zigzag direction. We also observe that the addition of K/Na atoms into the G/P system turns its semi-metallic nature into a metallic one. Moreover, we demonstrate that the intercalation of K/Na atoms within the G/P structure give low operating potentials of approximately 0.29 V for K and 0.58 V for Na. Thus, the nano-heterostructure can provide a theoretical storage capacity of 433 mAh/g and 580 mAh/g respectively for K and Na. Finally, the thermal stability of a fully potassiated/sodiated G/P system at room temperature is revealed by the ab-initio Molecular-Dynamics (AIMD) calculations. Considering all these properties, we conclude that the G/P nano-heterostructure can be considered as a good candidate for negative-electrode-materials for both K- and Na-ion batteries.