Highly Safe, Ultra‐Thin MOF‐Based Solid Polymer Electrolytes for Superior All‐Solid‐State Lithium‐Metal Battery Performance

Abstract Polyethylene oxide (PEO)/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is among the most promising candidates for developing solid polymer electrolytes (SPEs) for all‐solid‐state lithium‐metal batteries (ASSLMBs). However, practical applications of the PEO/LiTFSI system face challenges due to its relatively low ionic conductivity and low Li ⁺ transference number. To address these issues, a method is proposed that incorporates multiple components, including zeolitic imidazolate frameworks (ZIF‐67) as fillers and ionic liquid electrolytes (ILEs) as plasticizers, into a PEO/LiTFSI matrix. By optimizing the fabrication process, ultra‐thin membranes of the integrated electrolyte PEO/LiTFSI‐ILE‐ZIF‐67 (PLiZ) with a thickness of 32 µm are developed, achieving high ionic conductivity (1.19 × 10 ⁻⁴ S cm ⁻¹ at 25 °C), broad electrochemical stability (5.66 V), and high lithium‐ion mobility (0.8). As a result, the fabricated ASSLMBs exhibited excellent cycle stability at both room temperature and 60 °C, delivering an initial specific discharge capacity of 166.4 mAh g ⁻¹ and an impressive capacity retention of 83.7% after 1000 cycles at 3C under 60 °C, corresponding to a low fading rate of 0.0163% per cycle. Additionally, the designed SPEs demonstrated high safety properties, as shown by the successful cutting and folding of a working LiFePO ₄ /PLiZ/Li pouch cell. Therefore, this study presents a comprehensively improved method for developing high‐performance ASSLMBs.