A theoretical study of surface lithium effects on the [111] SiC nanowires as anode materials.

Abstract

Context: Silicon carbide nanowires (SiCNWs) are considered a promising alternative material for application in lithium-ion batteries, with researchers striving to develop new electrode materials that exhibit high capacity and high charge/discharge rate performance. To gain a deeper understanding of the application of SiCNWs in semiconductor material science and energy supply fields, we investigated the effects of nanoscale and surface lithiation on the electrical and mechanical properties of SiCNWs grown along the [111] direction. First-principles calculation was used to study their geometries, electronic structures, and associated electrochemical properties. Herein, we considered SiCNWs with full hydrogen passivation, full lithium passivation, and mixed passivation at different sizes. The formation energy indicates that the stability of SiCNWs increases with the increasing diameter, and the surface-lithiated SiC nanowires (Li-SiCNWs) are found to be energetically stable. The mixed passivated SiCNWs exhibit the properties of indirect band gap with the increase of lithium atoms on the surface, while the fully lithium passivated nanowires exhibit metallic behavior. Charge analysis shows that a portion of the electrons on the lithium atoms are transferred to the surface atoms of the nanowires and electrons prefer to cluster more near the C atoms. Additionally, Li-SiCNWs still have good mechanical resistance during the lithiation process. The stable open-circuit voltage range and theoretical capacity of these SiCNWs indicate their suitability as anode materials.

Method: In this study, Materials Studio 8.0 was used to construct the models of the SiCNWs. And all the density functional theory (DFT) calculations were performed by the Vienna ab initio Simulation Package (VASP). The self-consistent field calculations are performed over a Monkhorst-Pack net of 1 × 1 × 6 k-points. The energy convergence criteria for the self-consistent field calculation were set to 10^-5 eV/atom with a cutoff energy of 400 eV.