(714h) Self-Rearrangement of Si Particles in Si?C Composite Anodes during Cycling in Lithium-Ion Batteries: A Reactive Molecular Dynamics Study

Silicon−carbon (Si−C) composites have received great attention as promising anode materials for Li-ion batteries (LIBs), offering superior theoretical capacity with long-term stability. In this study, using molecular dynamics (MD) simulations with a reactive force field (ReaxFF), we investigate the atomistic lithiation behavior of Si particles coated by carbon structures, including cylindrical and planar graphitic pores with varying sizes. Our simulations reveal that during lithiation, disintegrated Si atoms migrate into the internal spaces of carbon pore with a critical size of 12.20 Å, which leads to the rearrangement of Si particles within the carbon coating. According to our ReaxFF-MD simulations, Li atoms adsorbed on carbon surfaces attract and interact with Si atoms, thereby facilitating their migration into carbon pores. Conversely, for carbon structures with smaller and larger pore sizes, Si diffusion into the pore spaces is restricted due to structural disparities between Si in the pore and bulk Li_xSi; therefore, the carbon coating primarily serves as a diffusion path for Li. Furthermore, during delithiation, Si atoms that have diffused into the carbon pore tend to cluster together, forming sub-nano-sized Si particles. These particles weakly bind with carbon surface thus can easily migrate into larger carbon pores, accelerating the redistribution of Si. While highlighting the crucial role of carbon pore size in determining the rearrangement of Si particles during cycling, this enhanced understanding provides valuable guidelines for the optimal design of Si−C anode structures.