Stable Oxyhalide‐Nitride Fast Ionic Conductors for All‐Solid‐State Li Metal Batteries

Rechargeable all-solid-state lithium metal batteries (ASSLMBs) utilizing inorganic solid-state electrolytes (SSEs) are promising for electric vehicles and large-scale grid energy storage. However, the Li dendrite growth in SSEs still constrains the practical utility of ASSLMBs. To achieve a high dendrite-suppression capability, SSEs must be chemically stable with Li, possess fast Li transfer kinetics, and exhibit high interface energy. Herein, a class of low-cost, eco-friendly, and sustainable oxyhalide-nitride solid electrolytes (ONSEs), denoted as Li_xN_yI_z-qLiOH (where x = 3y + z, 0 ≤ q ≤ 0.75), is designed to fulfill all the requirements. As-prepared ONSEs demonstrate chemically stable against Li and high interface energy (>43.08 meV Å^-2), effectively restraining Li dendrite growth and the self-degradation at electrode interfaces. Furthermore, improved thermodynamic oxidation stability of ONSEs (>3 V vs Li⁺/Li, 0.45 V for pure Li₃N), arising from the increased ionicity of Li─N bonds, contributes to the stability in ASSLMBs. As a proof-of-concept, the optimized ONSEs possess high ionic conductivity of 0.52 mS cm^-1 and achieve long-term cycling of Li||Li symmetric cell for over 500 h. When coupled with the Li₃InCl₆ SSE for high-voltage cathodes, the bilayer oxyhalide-nitride/Li₃InCl₆ electrolyte imparts 90% capacity retention over 500 cycles for Li||1 mAh cm^-2 LiCoO₂ cells.