Hexagonal Rodlike Cu-MOF-74-Derived Filler-Reinforced Composite Polymer Electrolyte for High-Performance Solid-State Lithium Batteries

Solid-state lithium batteries using solid composite polymer electrolytes (CPEs) with great thermal and mechanical stabilities are believed to be the next-generation advanced electrochemical devices, but they suffer from low ionic conductivity at room temperature and a poor interface between the electrode and the electrolyte. Herein, we present a poly­(ethylene oxide) (PEO)-based CPE allowing rapid Li⁺ migration enabled by coordinating the anions on the exposed metal sites of a metal–organic framework (MOF). The CPE contains MOF-74 fillers, a PEO matrix, and lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI). Owing to the strong anchoring effect of MOF-74 fillers on TFSI^– verified by calculations and measurements, the CPE exhibits a high ionic conductivity (5.5 × 10^–5 S·cm^–1 at 30 °C), a wide electrochemical stability (4.8 V), and an improved Li⁺ transference number (0.36). Besides, the adjusted local current density promotes the interfacial stability against the Li anode in a Li symmetric battery, which performed well at a current density of both 0.2 and 0.4 mA cm^–2. With these advantages, the all-solid-sate LiFePO₄ battery fabricated exhibited stable cycling performances (161 mA h g^–1 and maintained 152 mA h g^–1 after 300 cycles at 0.5 C). This strategy gives fresh reference to the utilization of different MOFs and polymers in building high-performance solid-state lithium batteries.