State-of-the-art Li- or Na-ion batteries typically use organic solvents in the electrolytes, which might cause serious safety issues. Replacing the liquid electrolytes with nonflammable, dense solid-state electrolytes can potentially solve this problem. Among all types of solid electrolytes, PEO-based polymer electrolytes (PBPEs) have attracted great attentions due to their excellent flexibility, chemical stability, and easiness for processing. In this talk, we will present our recent progress in development of flexible, Na-ion conducting PBPEs. In particular, we tried to incorporate various amounts of ionic liquid (i.e., PY₁₄FSI) into PEO + NaFSI electrolytes that can increase the amount of amorphous phase in the polymer and thus achieve higher ionic conduction. It was found that the highest conductivity was achieved with the composition of P(EO)₂₀NaFSI + 2.4PY₁₄FSI (2 x 10^-3 and 3 x 10^-4 S cm^-1 at 60^oC and RT with a Na⁺ transference number of ~0.1). We further verified the performance of the electrolyte with a composition of P(EO)₂₀NaFSI + 1.6PY₁₄FSI in symmetric and full cells. The critical current density of the electrolyte in Na symmetric cells was as high as 0.5 mA/cm² at 60^oC and the cells also showed an excellent stability during ~700 cycles at a current density of 0.1 mA/cm². A full cell with Na₃V₂(PO₄)₃ as the cathode showed an initial capacity of 100 mAh/g^-1 and a Coulombic Efficiency of ~94%. All of these demonstrated a PBPE with excellent chemical, mechanical, and electrochemical performance and properties for Na battery application.