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 mu m are developed, achieving high ionic conductivity (1.19 x 10-4 S cm-1 at 25 degrees 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 degrees 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 degrees 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 LiFePO4/PLiZ/Li pouch cell. Therefore, this study presents a comprehensively improved method for developing high-performance ASSLMBs. The introduction of polyhedral ZIF-67 particles and ionic liquid electrolytes (ILE) to the PEO/LiTFSI-based composite polymer electrolytes serves as important additives to enhance the properties of PEO polymer. Additionally, the optimization of the polymer electrolyte thickness significantly boosts the ionic conductivity, lithium-ion transference number, and overall performance of ASSLMB batteries. image