Stability of intermediate states in the surface lithiation process of silicene

Abstract

We have studied using density functional theory the Li-silicene system, mainly in the saturated region (0.11>X(Li)<1.0) which is critical to understand the solid electrolyte interface layer (SEI) formation. The electronic and vibrational properties of the intermediate states of lithiated silicene were calculated. Two models were used for the Li atoms on the silicene surface: Li on top of Si (perpendicular) and Li on top of the hexagon center (centered). The centered configurations have lower Eb values up to X(Li) = 0.33. However, the vibrational properties showed instabilities for lithium in the hexagon center. An intermediate state at X(Li) = 0.38 was found to be dynamically stable. A metallic to semiconductor transition is observed at X(Li) = 0.33, and X(Li) = 0.46. Few ordered vacancies or vacancies in the dilute region exhibit vibrational stability and gap opening. Elastic stiffness tensor for different concentrations of Li in the silicene-Li system were calculated, a critical concentration of X(Li)=0.333 was determined for the change of the mechanical properties behavior. silicel has a slightly higher 2D Young‘s moduli than silicene. However, vacancies in silicel produce a substantial decrement in mechanical properties.