Stable Room-Temperature Sodium–Sulfur Batteries via In-Situ Cross-Linked Functional Gel Polymer Electrolytes

Room-temperature sodium–sulfur batteries are recognized as a promising next-generation energy storage technology to meet the world’s growing energy demand. This system offers a compelling alternative to commercial lithium-ion batteries due to its lower cost, greater elemental abundance, and potentially higher energy density. However, the use of liquid electrolytes in sodium–sulfur batteries introduces several challenges that hinder practical application, including electrolyte leakage, sodium dendrite formation, and polysulfide shuttling. In our study, we developed a type of electrolyte designed to address these limitations. An in situ polymerized gel polymer electrolyte (GPE) with high conductivity, efficient Na+ transport, and stable sodium deposition was synthesized and characterized. Comprehensive physicochemical analyses were performed to evaluate the structural and thermal properties of the GPE, while electrochemical tests on both half- and full-cells were conducted to assess performance. The optimized GPE exhibited an ionic conductivity of 2.75 mS cm–1, a high sodium-ion transference number of 0.6, and a wide electrochemical stability window. The sodium–sulfur full-cell delivered an initial reversible discharge specific capacity of 498 mAh g–1 with 99.9% Coulombic efficiency, retaining 172 mAh g–1 after 200 cycles. Moreover, the GPE enabled stable sodium plating and stripping for almost 3000 h at a high current density of 0.1 mA cm–2 without short-circuiting. Our results demonstrate that the in situ polymerized gel polymer electrolyte is a strong candidate for room-temperature sodium–sulfur batteries, providing high ionic conductivity, excellent electrochemical stability, and enhanced cycling performance for next-generation energy storage applications.