A Comb-Chain Cross-Linker-Based Network Solid Polymer Electrolyte for All-Solid-State Sodium-Metal Batteries

All-solid-state sodium-metal batteries (SMBs) utilizing solid polymer electrolytes (SPEs) have gained considerable research interest due to the potentially enhanced safety, lower cost, and sustainable sodium supply compared to lithium metal. However, sodium's high reactivity makes it prone to dendrite and orphaned metal formation, reducing its capacity and efficiency. In this work, we report a comb-chain cross-linker-based network SPE for all-solid-state SMBs. The high-functionality macromolecular cross-linker offers excellent overall mechanical properties of the SPE. The polymer network exhibited an impressive elongation at break of 181% and a high toughness of 1.6 MJ m^-3. These excellent mechanical properties, combined with good ionic conductivity and processability, enable ultrathin SPE separators and contribute to the superb dendrite resistance and full cell performance of the SPE. Na|SPE|Na symmetric cells achieved a cycle life of ∼4248 h at 0.5 mA cm^-2 and 1 mAh cm^-2, while Na|SPE|P2-type Na_2/3[Ni_1/3Mn_2/3]-O₂ composite cathode full cells displayed 80.6% capacity retention after 700 cycles at 1C, both of which are the highest reported values among SPE-based all-solid-state SMBs. This excellent performance was attributed to the combined mechanical and electrochemical properties of the SPE.