Stress generation during anisotropic lithiation in silicon nanopillar electrodes: A reactive force field study

Highlights: • The approach incorporates the anisotropic migration of a sharp phase boundary. • The simulations capture prominent features of the two-phase anisotropic lithiation. • This work explains the geometric effect of the phase boundary on stress generation. -- Abstract: Models that are developed to investigate lithiation-induced stress in high-volume-change electrodes are often based on continuum approaches with simplifying assumptions. In this work, we investigate stress generation during the first lithiation of crystalline silicon electrodes solely using atomistic simulations with chemo-mechanical fidelity. We use a 〈100〉-oriented silicon nanopillar as a model system and perform molecular statics simulations with a reactive force field. The simulation approach incorporates the key physical feature of the lithiation – anisotropic formation and migration of an atomistically-sharp phase boundary. The resulting stress fields show the development of hoop tension near the nanopillar surface, which drives surface fracture at angular sites between two adjacent {110} facets. This work links the atomic-level physics of the lithiation directly with the stress generation and accounts for the geometric effect of the sharp phase boundary.