Energy Gap-Modulated Blue Phosphorene as Flexible Anodes for Lithium- and Sodium-Ion Batteries

Effective modulation of electronic and optical properties by virtue of external control might unfold an extensive variety of potential applications in nanoelectronics. In this context, first-principles density functional theory calculations have been evaluated to congregate additional data about the effects of strain on the electronic properties of blue phosphorene and enactment of this with regard to potential use in lithium-ion batteries/sodium-ion batteries. The adsorption of both Li and Na over unstrained blue phosphorene is very effective with adsorption energies of -1.77 and -1.05 eV, respectively. Incredibly, the application of both compressive and tensile strains causes significant strong binding of Li/Na atoms, with Li adsorption energies of -2.03 and -2.21 eV and Na adsorption energies of -1.19 and -1.49 eV for 10% compression and 10% stretch, respectively. The diffusion of these two alkali atoms over unstrained blue phosphorene is anisotropic, with an energy barrier of 0.09 eV for Li and 0.035 eV for Na in the zigzag direction and 0.350 eV for Li and 0.207 eV for Na in the armchair direction. Mere changes are observed in the diffusion of Li on the application of strain, whereas the Na diffusion barrier energy is extremely sensitive to the applied tensile strain both in zigzag and armchair directions. The band gap of monolayer blue phosphorene is calculated by Perdew-Burke-Ernzerhof (PBE) and the more accurate Heyd-Scuseria-Ernzerhof 06 (HSE06) method. The band gap of pristine phosphorene was found to be 2.24 eV based on PBE and 2.87 eV based on the HSE06 method, which indicates that monolayer blue phosphorene is a semiconductor. However, the band gap of phosphorene is observed to be strain tunable and has a reciprocative effect with biaxial strain. The material exhibits indirect-to direct band gap semiconductor at 10% tensile strain and semiconductor-to-semimetal transition at 10% compressive strain, whereas lithiation/sodiation induces a semiconductor-to-metal transition with unstrained phosphorene. These findings suggest that the applied strain is a robust and efficient approach to make blue phosphorene a promising material for achieving structural phase transition to meet the requirement of future electronic devices.