Enhancing Compatibility of Halide with Sulfide‐Electrolytes via High Oxygen Incorporation for Robust Solid‐State Batteries

Abstract Lithium‐metal‐halide (Li‐M‐X) solid‐state electrolytes (SSEs) offer significant potential for high‐energy‐density all‐solid‐state batteries (ASSBs) due to their high ionic conductivity, deformability, and compatibility with cathodes. However, to prevent direct reactions between halide SSEs and reductive anodes, sulfide SSEs are commonly used as interlayers in ASSBs. Yet, the chemical and electrochemical incompatibilities between halides and sulfides pose a new challenge. Here, a dual‐anion strategy is proposed and demonstrated to address this issue by introducing O 2− anions into the halide framework. These findings reveal that high‐concentration oxygen incorporation in Zr‐based halide SSEs can be achieved without compromising ion conductivity, while simultaneously reducing interfacial reaction energy with Li 6 PS 5 Cl sulfide SSEs. This results in the formation of a dense, low‐resistance Li 3 PO 4 ‐enriched interfacial layer, which contributes to superior electrochemical performance in full cells. ASSBs utilizing this electrolyte pair and a high‐loading LiCoO 2 cathode (19.3 mg cm −2 ) achieve an impressive areal capacity of 2.8 mAh cm −2 and stable cycling performance exceeding 400 cycles. The O/Cl dual‐anion strategy is also applicable to other halide SSEs paired with representative sulfide SSEs, including Li 6 PS 5 Cl, Li 10 GeP 2 S 12 , Li 3 PS 4 , Li 7 P 3 S 11, and Li 6.7 SiSb 0.5 S 5 I. This work provides valuable insights and strategies to improve the compatibility between halide and sulfide SSEs, advancing the development of ASSBs.