Polymer gel electrolytes containing sodium salts with BF4−, ClO4− and CF3SO3− anions immobilized in TEGDME molecular liquid for sodium battery and electric double layer capacitor

The present study reports synthesis and analysis of different characteristics of sodium ion conducting polymer gel electrolytes (PGEs) containing sodium salts with BF4−, ClO4− and CF3SO3− anions dissolved in tetraethylene glycol dimethyl ether and immobilized in a copolymer matrix consisting of polymethyl methacrylate and poly(vinylidene fluoride-co-hexafluoropropylene). The PGE containing the NaBF4 salt could deliver an ionic conductivity of 1.4 × 10−3 S cm−1 at room temperature along with superior dielectric properties as compared to the electrolytes with NaClO4 and NaCF3SO3 salts. The feasibility of designing sodium-based batteries and EDLCs has been demonstrated using the optimized PGE containing NaBF4 salt. The prototype sodium‑sulfur (NaS) battery designed by utilizing the optimized PGE, sodium amalgam anode and sulfur cathode provides open circuit voltage of ∼2.4 V and initial discharge capacity of ∼163 mA h g−1 and 126 mA h g−1 at discharge currents of 33 mA g−1 and 66 mA g−1, respectively. This optimized PGE also demonstrate good compatibility with AC electrodes in electric double layer capacitor (EDLC) application and delivered a significant specific capacity ∼64 F g−1 at 0.5 mA cm−2 current.