Role of surface Li vacancies on the moisture stability of Li10SiP2S12 solid electrolyte: Insights from first-principles calculations

Sulfide-based solid-state electrolytes (SSEs) play a crucial role in the development of all-solid-state lithium-ion batteries (ASSLBs). However, their susceptibility to hydrolysis under humid conditions, leading to the release of toxic H₂S gas, severely limits practical applications. Elemental substitution has been widely used to enhance both the ionic conductivity and chemical stability of sulfide SSEs. Additionally, lithium vacancies have been shown to increase Li-ion conductivity, yet their effect on the moisture stability of sulfide SSEs remains insufficiently explored. In this study, we investigate the effect of Li-vacancies on the moisture stability of Li₁₀SiP₂S₁₂(LSiPS), a model sulfide SSE, using density functional theory (DFT) calculations. Our findings reveal that Li vacancies on the Li₁₀SiP₂S₁₂ (v-LSiPS), surface significantly raise the energy barrier for H₂S formation, indicating a considerable enhancement in moisture stability. Detailed bond length analyses and electron density difference (EDD) calculations demonstrate strengthened P-S bonds in the presence of Li vacancies, providing a mechanistic basis for improved stability. These insights offer valuable guidance for designing more robust sulfide-based SSEs suitable for real-world ASSLB applications.