Enhanced Gel Polymer Electrolytes for room temperature Sodium-Sufur Batteries

Abstract

The growing demand for safe, sustainable, and high–energy–density energy storage systems has intensified research into room-temperature sodium–sulfur (RT Na–S) batteries. Despite their advantages, their practical application is hindered by the polysulfide shuttle effect, which causes active material loss, low sulfur utilization, and rapid capacity degradation. This study addresses the research question: how does variation in the concentration of metal–organic framework (ZIF-8) influence ionic conductivity, interfacial stability, and polysulfide suppression in gel polymer electrolytes for RT Na–S batteries? Gpe membranes were fabricated using a poly(ethylene oxide)/poly(vinylidenefluoride-co-hexafluoropropylene) matrix with sodium triflate as the conducting salt and propylene carbonate as the plasticizer, followed by swelling in 1 M NaOTf in diglyme electrolyte. Systematic variation of ZIF-8 content reveals a strong dependence of electrolyte properties on filler concentration. Among the investigated compositions, Gpe 4% exhibits the most optimized performance, achieving a favorable balance between ionic conductivity, mechanical strength, and suppression of polysulfide migration, attributed to enhanced polymer chain mobility and the adsorption capability of the porous framework. Comprehensive structural, morphological, thermal, and electrochemical analyses confirm effective filler integration and improved electrolyte properties. Electrochemical evaluation demonstrates that Gpe systems exhibit superior performance compared to the commercial Celgard 2500 polypropylene separator in Na//S coin cells, with Gpe 4% delivering the best results in terms of capacity retention, Coulombic efficiency, and cycling stability. Overall, this work establishes that controlled incorporation of ZIF-8 provides a rational strategy for simultaneously enhancing ion transport and mitigating shuttle effects, offering a promising pathway for the development of high-performance room-temperature Na–S batteries.