Optimization of PEO-Based Polymer Electrolytes as an Intermediate for the Na-β″-Al₂O₃/Na₃V₂(PO₄)₃ Positive Electrode

This study explores the influence of sodium bis(fluorosulfonyl)amide (NaFSA) concentration and the incorporation of the anion acceptor, 2,4,6-triphenylboroxin (TPB), on the performance of poly(ethylene oxide) (PEO)-based polymer electrolytes for solid-state sodium batteries. Raman spectroscopy confirmed that NaFSA remains partially dissociated in the polymer matrix, independent of the salt concentration. Electrochemical impedance spectroscopy and temperature-dependent conductivity analyses revealed that ionic conductivity is governed by both salt concentration and polymer phase transitions, particularly around 50 °C. Optimal performance was achieved at a NaFSA ratio of 1/30, which provided a favorable balance between ion availability and minimized anion-induced polarization. The addition of TPB significantly enhanced sodium-ion transference numbers and high-rate charge–discharge capabilities, especially at lower salt concentrations, by effectively trapping anions and reducing both bulk and interfacial resistances. These results underscore the importance of tailoring the salt concentration and incorporating functional additives to optimize ion transport in polymer electrolytes, offering a promising approach for advancing solid-state sodium battery technologies.