Gel polymer electrolytes for room-temperature sodium sulfur batteries

Abstract

Sodium sulfur batteries have gained attention owing to their advantages of low cost and high specific capacity. However, the current electrolytes have a few main disadvantages including sodium-dendrite growth, sulfur shuttling and electrolyte leakage, which hinder their practical application. Herein, we report the preparation of poly(vinylidene fluoride-co-hexafluoropropylene)-based gel polymer electrolytes using a simple solution casting technique for room-temperature sodium sulfur battery applications. The gel polymer electrolyte was activated by soaking the freshly prepared gel polymer membranes in a liquid electrolyte solution. Our gel polymer electrolyte exhibited a high ionic conductivity of 1.37 mS cm⁻¹ at ambient temperature, with an electrochemical stability window of 4.5 V versus Na⁺/Na. Furthermore, sodium symmetric cells showed stable stripping/plating of Na⁺ up to 3000 hours, with a transference number of 0.648. The cells achieved a specific capacity of 398 mA h g⁻¹ for the initial reversible discharge specific capacity and 75 mA h g⁻¹ at cycle 200 with 99.9% coulombic efficiency at 0.1 C rate. Our results demonstrate that these polymer electrolytes are potential candidates for sodium sulfur batteries with desired performance.