ReaxFF Molecular Dynamics Simulations on Silicon Suboxide as Anode Material for Lithium-Ion Batteries

Amorphous silicon suboxides (a-SiOy, y < 2) have attracted much attention as promising anode materials for rechargeable energy storage devices. We performed ReaxFF molecular dynamics simulations (ReaxFF MD) to examine the structural evolution, volume expansion, and diffusion properties in amorphous LixSiOy bulks, and to reveal the impact of oxygen content on its performance. Our results suggest that the inserted Li atoms preferentially disintegrate Si–Si connections in Si-rich oxide (a-SiO0.5), while they tend to break Si–O connections in O-rich silicon oxide (a-SiO). Besides, our study demonstrates that a higher concentration of O atoms in a-SiOy reduces its relative expansion upon lithiation, which is desirable for the application of electrode materials. However, we also find that the diffusion properties weaken with increasing O content. At the same level of O concentration, the diffusion coefficient of Li atoms () increases with lithiation, while at the same level of Li concentration, decreases with the increasing of O content. Our simulation results provide important insights into the role of O in a-SiOy at the atomistic level.