Atomic-level Insights into the Highly Conductive Lithium Thio-phosphate Solid Electrolytes with Exceptional Stability Against Lithium Metal

Abstract

Despite the wide range of emerging solid electrolytes with promising characteristics, such as high ionic conductivity, the inherent thermodynamic instability against lithium metal remains a significant challenge. We have previously introduced a new family of solid electrolytes based on thiophosphates with inherent stability against metallic Li anode and high conductivity [Szczuka et al., JACS, 2022, 144 (36)]. In this study, we employ density functional theory (DFT) together with ab initio molecular dynamics (AIMD) simulations to investigate the diffusion mechanisms and underlying factors contributing to the high ionic conductivity of these novel Li-P-S ternary electrolytes, including Li7PS2, Li5PS, Li8P2S, and Li11P3S. Our findings reveal that these materials exhibit ionic conductivities comparable to the well-known superionic conductor, Li7P3S11, positioning them as promising candidates for solid-state battery applications. Additionally, we show that, unlike Li7P3S11 which forms a solid-electrolyte interphase, the novel Li-P-S ternaries exhibit remarkable stability against Li metal anode due to their unique Li2S-like structural framework. The absence of a solid-electrolyte interphase layer is particularly significant, as it eliminates additional resistance at the electrolyte-anode interface, a common challenge in many solid-state battery systems. Our study not only highlights the suitability of these novel ternaries, particularly Li5PS, as high-performance solid electrolytes but also underscores the importance of structural design in developing next-generation battery materials. The ability of these materials to maintain high ionic conductivity and stability over extended periods makes them ideal candidates for future solid-state lithium batteries, offering a pathway to safer, more efficient, and longer-lasting energy storage solutions.