Hot-Pressing Enhances Mechanical Strength of PEO Solid Polymer Electrolyte for All-Solid-State Sodium Metal Batteries

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) are widely utilized in all-solid-state sodium metal batteries (ASSSMBs) due to their excellent flexibility and safety. However, poor ionic conductivity and mechanical strength limit its development. In this work, an emerging solvent-free hot-pressing method is used to prepare mechanically robust PEO-based SPE, while sodium superionic conductors Na₃Zr₂Si₂PO₁₂ (NZSP) and NaClO₄ are introduced to improve ionic conductivity. The as-prepared electrolyte exhibits a high ionic conductivity of 4.42 × 10^-4 S cm^-1 and a suitable electrochemical stability window (4.5 V vs Na/Na⁺). Furthermore, the SPE enables intimate contact with the electrode. The Na||Na₃V₂(PO₄)₃@C ASSSMB delivers a high-capacity retention of 97.1% after 100 cycles at 0.5 C and 60 °C, and exhibits excellent Coulombic efficiency (CE) (close to 100%). The ASSSMB with the 20 µm thick electrolyte also demonstrates excellent cyclic stability. This study provides a promising strategy for designing stable polymer-ceramic composite electrolyte membranes through hot-pressing to realize high-energy-density sodium metal batteries.