Abstract: Solid-state sodium-ion batteries (SSSIBs) are widely recognized as a primary candidate for the next generation of high-performance energy storage technologies. However, the low ionic conductivity of solid electrolytes and the high interface charge transfer impedance remain urgent challenges for SSSIBs. This study describes the construction of a flexible solid polymer Ca@SA/ZIF-8-PEO solid-state electrolyte via the electrospinning technique. The electrolyte has great mechanical strength, excellent flame qualities, high Na⁺conductivity (4.4 × 10^-4 S cm^-1) and high Na⁺ migration number (0.45). Comprehensively experimental results demonstrate that the combination of zeolitic imidazolate framework-8 (ZIF-8) and Ca²⁺ cross-linked sodium alginate (SA) can synergistically decrease the crystallinity of poly(ethyleneoxide) (PEO), provide more active sites for the adsorption of sodium ions, and promote the migration of sodium ions. COMSOL simulations and X-ray photoelectron spectroscopy (XPS) results demonstrate that the ZIF-8 nanoparticles and Ca@SA could alleviate the Na⁺ concentration polarization and promote the uniform deposition of sodium on the surface of the Na anode, which stabilized the solid electrolyte interface (SEI) layer. In view of the abovementioned merits, after assembling the Na/Ca@SA/ZIF-8-PEO SPE/Na symmetric cell, it not only achieves a stable cycle of approximately 1500 h with uniform Na deposition and dissolution at the Na electrode interface, but also delivers the high electrochemical window (4.85 V). In addition, the assembled NVP/Ca@SA/ZIF-8-PEO SPE/Na all-solid-state battery delivers a specific capacity of 92 mAh g^-1 after almost 1000 cycles at 1 C current density. Therefore, the proposed Ca@SA/ZIF-8-PEO SPE provides new insights for further fabrication and engineering applications of SSSIBs.

Key words: Solid state battery, Solid electrolyte, PEO, ZIF-8, Sodium ion battery