Lewis Acid and Hydroxyl Enabled PEO Electrolytes for Solid-State Lithium Metal Batteries
Poly(ethylene oxide) (PEO)-based solid polymer electrolytes are leading candidates for solid-state lithium metal batteries due to their flexibility, processability, and interfacial compliance. However, the strong crystallization tendency of PEO and limited lithium salt dissociation result in low ionic conductivity and low Li+ transference number, exacerbating concentration polarization and interfacial instability. Introducing metal-organic framework (MOF) fillers into PEO matrices has emerged as an effective route to regulate polymer-chain packing and promote salt dissociation via Lewis acid-base interactions. Yet, most studies focus on cubic ZIF-8, whose saturated Zn coordination environment limits intrinsic Lewis acidity and restricts its ability to immobilize TFSI- anions. Simultaneously, simple physical blending often leaves discontinuous interfacial transport regions in composite electrolytes, so improved salt dissociation does not automatically translate into fast Li+ transport. Here we report a PEO-based composite polymer electrolyte, denoted as PZS, that couples monoclinic ZIF-8 (M-ZIF-8) nanosheets with a thin SiO2 layer. The design combines two complementary functions: the under-coordinated Zn sites in M-ZIF-8 provide strong Lewis acid centers to adsorb TFSI- and promote LiTFSI dissociation, while the hydroxyl-rich SiO2 shell improves compatibility with the PEO matrix and helps construct continuous interfacial Li+ transport pathways. Benefiting from this synergy, the optimized PZS electrolyte delivers an ionic conductivity of 8.3 × 10-4 S cm-1 and a Li+ transference number of 0.57 at 60 ℃, together with an electrochemical stability window of 5.2 V. Li||Li symmetric cells remain stable for over 1200 h at 0.1 mA cm-2, and LFP||Li full cells retain 80% of their capacity after 400 cycles at 0.5 C.