Computational Discovery of Li ₆ PO ₅ I: An Oxide Argyrodite for Solid-State Electrolytes

The development of stable and high-performance solid-state electrolytes (SSEs) is essential for next-generation, all-solid-state lithium batteries. In this work, we computationally predict and characterize an oxide-based lithium argyrodite as a perspective solid-state electrolyte, Li6PO5I, using first-principles calculations and machine-learned interatomic potentials. Three iodine site configurations were examined: fully ordered (4a/0c) and partially disordered (3a/1c and 2a/2c). While the ordered 4a/0c phase exhibits low ionic conductivity (∼0.001 mS/cm), configurational disorder significantly enhances lithium transport. The 3a/1c and 2a/2c structures demonstrate ionic conductivities of 0.2 and 3.3 mS/cm, respectively, at 300 K with 2% Li vacancies, attributed to increased intercage hopping facilitated by iodine occupation of 4c sites. The thermodynamic, mechanical, and dynamic stability of all metastable phases was confirmed through convex hull analysis, elastic tensor calculations, and phonon dispersion. Ab initio molecular dynamics revealed a thermal stability up to 1400 K. A wide (3 V) electrochemical stability window and water tolerance further support Li6PO5I, particularly in disordered configurations, as a promising SSE candidate. This work underscores the critical role of site disorder in optimizing the ionic conductivity in oxide-based electrolytes.