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 anions, facilitating the Na ion dissociation from salt. Simultaneously, the well-defined nanopores within ZIF-8 particles provide oriented and ordered migration channels for Na migration. As a result, this pioneering design allows the solid polymer electrolyte to achieve 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 4.89 V vs. Na/Na⁺. 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. This innovative polymer-in-MOF design offers a compelling strategy for advancing high-performance and safe solid-state metal battery technologies.