A first-principles study of bilayered black phosphorene as a potential anode material for sodium-ion batteries

Black phosphorene has attracted widespread attention because of its great potential as a high-performance anode material for sodium-ion batteries (SIBs). However, almost all theoretical studies on sodium (Na) atom adsorption and diffusion in it have not taken temperature into account. Actually, the structural stability of an anode material at room temperature is vital in practical applications. In this work, employing first-principles calculations, we investigate the stability of AA-, AB-, AC- and AD-stacked bilayered black phosphorene (BBP) at ground state, and Na adsorption and diffusion within BBPs. Using ab initio molecular-dynamics (AIMD) calculations, dynamic stabilities of pristine BBP and Na-adsorbed BBP systems at room temperature are discussed. Our calculations show that only AB-stacked BBP is stable. Na atoms generally prefer to intercalate within BBP, making all BBPs exhibit metallic properties, which provides good electrical conductivity required for an ideal anode of SIBs. In particular, our AIMD results indicate that the temperature effect on the structural stability of Na-adsorbed BBP could not be neglected. It increases Na capacity loss at room temperature. This provides an important reference for further theoretical and experimental exploration of anode materials for SIBs. Additionally, the AC-stacked structure facilitates Na intercalation within BBP, and Na diffusion exhibits a strong directional preference, diffusing very fast along the zigzag direction. Our results suggest that AC-stacked BBP is a potential anode material of SIBs.