A New Quasi-Solid Polymer Electrolyte for Next-Generation Na-O Batteries: Unveiling the Potential of a Polyamide-Polyether System.

A novel quasi-solid polymer electrolyte (QSPE) composed of polyamide (PA) and polyethylene oxide (PEO), commercially known as Pebax1657, and combined with 1 M sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) in diethylene glycol dimethyl ether (diglyme, DEGDME), has been investigated for sodium-oxygen (Na-O) batteries. Pebax1657 QSPE exhibits high ionic conductivity (6.57 × 10 S cm at room temprerature - RT), an oxidation onset potential of 4.69 V versus Na/Na⁺, and an enhanced Na⁺ transference number (t ≈ 0.40). Structural analysis (Raman spectroscopy, differential scanning calorimetry, X-ray diffraction, small-angle X-ray scattering) confirms reduced PEO crystallinity and formation of orderly nanodomains, facilitating Na⁺ transport. Long-term galvanostatic cycling in Na|Na symmetrical cells demonstrates stable overpotentials (≈80 mV) at 75 µA cm⁻ for 210 h, outperforming conventional liquid electrolytes (≈110 h). Pebax1657 QSPE enables higher discharge capacities (2.60 mAh cm⁻ at 75 µA cm⁻; 2.11 mAh cm⁻ at 150 µA cm⁻) with lower overpotentials (≈0.2 V). It sustains 25 cycles at 75 µA cm⁻ and 35 cycles at 150 µA cm⁻ at 0.25 mAh cm⁻, with a Coulombic Efficiency (CE) of 80-90%. Compared to the state of the art, Pebax1657 QSPE offers improved electrochemical stability, lower overpotentials, and better capacity retention. Its sustainability and versatility make it a strong candidate for Na-O batteries and other energy storage applications.