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, we design 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) to fulfil all the requirements. As‐prepared oxyhalide‐nitride fast conductors demonstrate chemically stable against Li and high interface energy (> 43.08 meV Å⁻²), effectively restraining Li dendrite growth and the self‐degradation at the LMA interfaces. Furthermore, improved thermodynamic oxidation stability of ONSEs (> 3 V versus 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 bi‐layer oxyhalide‐nitride/Li₃InCl₆ electrolyte imparts 90% capacity retention over 500 cycles for Li||1 mAh cm⁻² LiCoO₂ cells. This work heralds a class of stable ONSEs with exceptional Li compatibility, good oxidative resistance, as well as high ionic conductivity to significantly ASSLMBs advance.

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