Ultrathin PTFE-Supported Composite Polymer Electrolyte Enabled by Metal–Organic Framework-Assisted Dual-Salt Regulation for Solid-State Lithium Metal Batteries

Developing safe and high-energy solid-state lithium metal batteries (LMBs) remains challenging due to the need to simultaneously achieve ultrathin electrolyte membranes, fast ion transport, and mechanical robustness. Herein, we report a scalable 19 μm composite electrolyte based on a porous PTFE scaffold, a PEO/LiTFSI matrix, and LiClO₄-associated UiO-66-NH₂ as a functional filler. In this metal–organic framework (MOF)-assisted dual-salt regulation strategy, LiTFSI is dispersed in the polymer matrix, while LiClO₄ is pre-associated with the amino-functionalized UiO-66 to regulate the local Li⁺ environment. The synergistic effects of the MOF filler and dual salts reduce PEO crystallinity and promote more efficient Li⁺ transport. The porous PTFE scaffold further enables membrane thinning and mechanical reinforcement. As a result, the electrolyte exhibits an ionic conductivity of 2.19 × 10⁻⁴ S cm⁻¹ at 60 °C, an electrochemical stability window of 4.6 V, a Li⁺ transference number ($$) of 0.69, and a tensile strength of 70 MPa. LiFePO₄ cells deliver stable cycling with 97% capacity retention after 160 cycles, and good rate capability and compatibility with high-voltage NCM523 cathodes are also demonstrated. This work provides a practical MOF-assisted ion-regulation strategy for designing ultrathin and mechanically robust polymer electrolytes for advanced solid-state batteries.