Three-Dimensional Metal–Organic Framework@Cellulose Skeleton-Reinforced Composite Polymer Electrolyte for All-Solid-State Lithium Metal Battery

High-safety and high-energy-density solid-state lithium metal batteries (SSLMBs) attract tremendous interest in both academia and industry. Especially, composite polymer electrolytes (CPEs) can overcome the limitations of single-component solid-state electrolytes. In this work, a strategy of combining a rigid functional skeleton with a soft polymer electrolyte to prepare reinforced CPEs was adopted. The in situ grown zeolitic imidazolate frameworks (ZIFs) with three-dimensional cellulose fiber skeleton (ZIF-67@CF) and succinonitrile (SN) plasticizer into poly(ethylene oxide) (PEO) together form ZIF-67@CF/PEO-SN CPEs. The addition of ZIF-67@CF and SN to PEO synergistically enhanced the physical and electrochemical properties of CPEs. Furthermore, the conduction mechanism of lithium-ion (Li⁺) in CPEs was studied using density functional theory. It is impressive that the ZIF-67@CF/PEO-SN CPEs at 30 °C exhibit a high ionic conductivity of 1.17 × 10^-4 S cm^-1, a competitive Li⁺ transference number of 0.40, a wide electrochemical window of 5.0 V, a notable tensile strength of 18.7 MPa, and superior lithium plating/stripping stability (>550 h at 0.1 mA cm²). Such favorable features endowed LiFePO₄/(ZIF-67@CF/PEO-SN)/Li cell at 30 °C with a high discharging capacity (152.5 mA h g^-1 at 0.2 C), a long cycling lifespan (>150 cycles with 99% capacity retention), and superior operating safety. This work provides insights and promotes the application of functionalized CPEs for SSLMBs.