Enhancing Sodium Ion Transport in a PEO-Based Solid Polymer Electrolyte System with NaAlO₂ Active Fillers

This work reports the effect of sodium aluminate (NaAlO₂) filler particles on the ion dynamics of a solid polymer electrolyte system comprising polyethylene oxide, sodium perchlorate (NaClO₄) and propylene carbonate. Free-standing flexible polymer electrolyte films were obtained by solution-casting technique. The effect of NaAlO₂ fillers in the Na⁺ transport in the electrolyte system has been investigated using various physical and electrochemical studies. Scanning electron microscopy and X-ray diffraction studies reveal the enhanced amorphicity of the polymer electrolyte system upon dispersion of NaAlO₂ fillers. The undispersed polymer electrolyte displays a maximum ionic conductivity of 1.6 × 10⁻⁵ S cm⁻¹ at 25°C, which increases to 7.4 × 10⁻⁵ S cm⁻¹ on dispersion of 5 wt.% NaAlO₂ fillers at 30°C. The ion mobility and enhanced free ion numbers in the dispersed polymer electrolyte system are well-observed in the frequency-dependent dielectric studies. The optimized composition shows a significantly improved Na⁺ transport number of ~ 0.60 and electrochemical stability window of ~ 4.5 V.