Atomistic observation of the lithiation and delithiation behaviors of silicon nanowires using reactive molecular dynamics simulations

Abstract

In this talk, we will discuss the mechanisms for the lithiation and delithiation of Si NWs determined using a large-scale molecular dynamics (MD) simulation with a reactive force field (ReaxFF). The ReaxFF is developed using results from first-principles calculations for various crystals and molecules. During the lithiation process, Li atoms penetrate into the lattices of the crystalline Si (c-Si) NWs preferentially along the <110> or <112> direction, and then the c-Si changes into amorphous LixSi (a-LixSi) phases due to the simultaneous breaking of Si-Si bonds as a result of the tensile stresses between Si atoms. Before the complete amorphization of the Si NWs, we observe the formation of silicene-like structures in the NWs that are eventually broken into low-coordinated components, such as dumbbells and isolated atoms. Additionally, during delithiation of LixSi NWs, we observe the formation of a small amount of c-Si nuclei in the a-LixSi matrix below a composition of Li1.4Si ~ Li1.5Si, and we demonstrate that the two-phase structure can be thermodynamically more favorable than the single-phase a-LixSi.