A flexible and free-standing composite solid electrolyte with a pomegranate-like structure for solid-state sodium-ion batteries

Solid sodium-ion batteries have the advantages of high energy density and good safety and are considered promising candidates for the next generation of energy storage systems. However, the sizeable interfacial resistance and dendrite growth between sodium and solid electrolytes, especially at high current densities, severely limit their development. Polymer-ceramic composite electrolytes are considered one of the potential candidates for solid electrolytes with high ionic conductivity and soft interface contact. In this study, a flexible self-supporting composite solid electrolyte with a pomegranate structure was prepared by a simple solution casting method. The addition of Na3Zr2Si2PO12 filler significantly improved the mechanical strength and electrochemical stability of the composite polymer electrolyte (CPE). The electrochemical stability window increases to 4.8 V relative to Na/Na+, and the conductivity reaches 1.069 × 10−4 S cm−1 at room temperature. Solid-state Na3V2(PO4)3/Na batteries using this CPE exhibit high cycle stability, with a high capacity retention rate at 1C (95.13%, coulomb efficiency of >98% after 290 cycles). These results indicate that PVDF-based CPE doped with inorganic Na3Zr2Si2PO12 packing is a promising composite electrolyte for solid sodium-ion batteries.