Anisotropic Swelling and Fracture of Silicon Nanowires during Lithiation

TLDR

Anisotropic swelling of Si nanowires during lithiation arises from interfacial accommodation of large volumetric strains that depend on crystallographic orientation, leading to a dumbbell‑shaped cross section via plastic flow and necking instability driven by tensile hoop stress. The resulting plasticity‑driven morphological instabilities frequently cause fracture of lithiated nanowires, as captured in video, providing key insights into battery degradation mechanisms.

Abstract

We report direct observation of an unexpected anisotropic swelling of Si nanowires during lithiation against either a solid electrolyte with a lithium counter-electrode or a liquid electrolyte with a LiCoO2 counter-electrode. Such anisotropic expansion is attributed to the interfacial processes of accommodating large volumetric strains at the lithiation reaction front that depend sensitively on the crystallographic orientation. This anisotropic swelling results in lithiated Si nanowires with a remarkable dumbbell-shaped cross section, which develops due to plastic flow and an ensuing necking instability that is induced by the tensile hoop stress buildup in the lithiated shell. The plasticity-driven morphological instabilities often lead to fracture in lithiated nanowires, now captured in video. These results provide important insight into the battery degradation mechanisms.