Unveiling Solid Electrolyte Interphase Formation in All-Solid-State Batteries—Computational Insights into Li-Metal/Electrolyte Interfaces at the Molecular Level

Solid-state ionic conductors are crucial for advancing energy storage technologies, particularly all-solid-state batteries (ASSBs). These materials offer high ionic conductivity and stability, but realizing their full potential in high-performance electrochemical devices requires a deep understanding of ionic mobility and reactivity at interfaces. Our research delves into the intricate interfacial phenomena of halide- and sulfide-based solid electrolytes with lithium metal, using advanced atomistic modeling integrated with cutting-edge characterizations to provide new insights and guide next-generation battery design. Specifically, we highlight critical enhancements in modeling capabilities through diverse case studies that combine ab initio molecular dynamics (AIMD) with machine-learned potentials to address real-world complexities beyond idealized systems [1-4].<br/><br/>We first explore Li₃YCl₄Br₂, known for its high ionic conductivity, ductility, and electrochemical stability. Yet, reactivity with lithium metal can form secondary compounds, hindering practical utility. Through a combination of physico-chemical and electrochemical characterizations with AIMD simulations, we have studied the Li/electrolyte interface's dynamics and evolution during cycling. We find that reaction products form a structured SEI with mixed ionic and electronic conductivity, crucial for a cells' outstanding cycling stability. In particular, this SEI structure enables symmetric cells with Li₃YCl₄Br₂ and bare Li-metal electrodes to withstand 1000 hours of Li electrodeposition-dissolution with low overpotential.<br/><br/>Furthermore, expanding AIMD simulations, we use machine-learned interatomic potentials to simulate SEI growth for Li₆PS₅Cl on unprecedented time and length scales. These simulations reveal a two-step growth mechanism: an initial chemical reaction forming an amorphous phase, followed by a slower crystallization into a 5Li₂S-Li₃P-LiCl solid solution [4]. This detailed understanding supports recent experimental hypotheses and sheds light on complex SEI evolution processes.<br/><br/>Overall, by elucidating atomic-level processes and their impact on macroscopic properties, we demonstrate how advanced modeling techniques can optimize solid-state battery performance, guiding the development of more effective energy storage solutions.<br/><br/><b>REFERENCES</b><br/>[1] A. Golov, J. Carrasco, <i>ACS Appl. Mater. Interfaces </i><b>2021</b>, 13, 43734.<br/>[2] A. Golov, J. Carrasco, <i>npj Comput. Mater.</i> <b>2022</b>, 8, 187.<br/>[3] A. Golov, J. Carrasco, <i>ACS Energy Lett.</i> <b>2023</b>, 8, 4129.<br/>[4] G. Chaney <i>et al</i>., <i>ACS Appl. Mater. Interfaces </i><b>2024</b> 16, 24624.