Confining Polymer Electrolyte in MOF for Safe and High‐Performance All‐Solid‐State Sodium Metal Batteries

Nanoconfined polymer molecules exhibit profound transformations in their properties and behaviors. Here, we present the synthesis of a polymer‐in‐MOF single ion conducting solid polymer electrolyte, where polymer segments are partially confined within nanopores ZIF‐8 particles through Lewis acid‐base interactions for solid‐state sodium‐metal batteries (SSMBs). The unique nanoconfinement effectively weakens Na ion coordination with the polymer matrix, enhancing the Na ion dissociation kinetics. Simultaneously, the well‐defined nanopores within ZIF‐8 particles serve as nanoconfined ion migration channels, enabling rapid Na ion transport. As a result, this pioneering design enables the solid polymer electrolyte to achieve remarkable metrics, including a Na ion transference number of 0.87, Na ion conductivity of 4.01×10‐4 S cm‐1, and an extended electrochemical voltage window up to 4.8 V vs. Na/Na+ at 80 °C. The assembled SSMBs (with Na3V2(PO4)3 as the cathode) exhibit dendrite‐free Na‐metal deposition, promising rate capability, and stable cycling performance with 96% capacity retention over 300 cycles at 80 °C. This innovative polymer‐in‐MOF design offers a compelling strategy for advancing high‐performance and safe solid‐state metal battery technologies.