Prediction of Cyclic Stress-Induced Mechanical Failure in Sulfide-Based Solid Electrolytes: A Reactive Molecular Dynamics Study

Cell failure due to crack formation and subsequent lithium dendrite penetration is well-known to hinder the utilization of sulfide solid-state electrolytes (SSEs), such as Li 3 PS 4 (LPS), with Li metal. However, the underlying mechanisms responsible for crack formation and evolution in LPS are still poorly understood. Herein, we investigated the structural evolution of LPS under cyclic stress conditions by employing a reactive force field, developed in conjunction with first-principles calculations. Our results clearly demonstrate unmitigated void generation and coalescence associated with amorphous phase formation in LPS over the course of stress cycling. This mechanical degradation behavior is attributed to the distortion and densification of the sulfide material during cyclic strain conditions. Moreover, the impact of disordered-amorphous structures and pre-existing microvoids on the mechanical behavior of LPS is systemically studied, suggesting that such structures could further facilitate electrolyte deterioration under even lower stress conditions. These findings provide insights into the origin and evolution of mechanical degradation in sulfide SSEs.