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

Abstract 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 x N y I z ‐ q LiOH (where x = 3 y + 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 Li 3 N), 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 Li 3 InCl 6 SSE for high‐voltage cathodes, the bilayer oxyhalide‐nitride/Li 3 InCl 6 electrolyte imparts 90% capacity retention over 500 cycles for Li||1 mAh cm −2 LiCoO 2 cells.