Unveiling Solid Electrolyte Interphase Formation at the Molecular Level: Computational Insights into Bare Li-Metal Anode and Li₆PS_5-x Se_x Cl Argyrodite Solid Electrolyte

The development of high-energy-dense, sustainable all-solid-state batteries faces a major challenge in achieving compatibility between the anode and electrolyte. A promising solution lies in the use of highly ion-conductive solid electrolytes, such as those from the argyrodite family. Previous studies have shown that the ionic conductivity of the argyrodite Li6PS5Cl can be significantly enhanced by partially substituting S with Se. However, there remains a lack of fundamental knowledge regarding the effect of doping on the interfacial stability. In this study, we employ long-scale ab initio molecular dynamics simulations, which allowed us to gain unprecedented insights into the process of solid electrolyte interface (SEI) formation. The study focuses on the stage of nucleation of crystalline products, enabling us to investigate in silico the SEI formation process of Se-substituted Li6PS5Cl. Our results demonstrate that kinetic factors play a crucial role in this process. Importantly, we discovered that selective anionic substitution can accelerate the formation of a stable interface, thus potentially resolving anode-electrolyte compatibility issues.