Triglyme-based electrolyte for sodium-ion and sodium-sulfur batteries

Herein, we investigate a lowly flammable electrolyte formed by dissolving sodium trifluoromethanesulfonate (NaCF3SO3) salt in triethylene glycol dimethyl ether (TREGDME) solvent as suitable medium for application in Na-ion and Na/S cells. The study, performed by using various electrochemical techniques, including impedance spectroscopy, voltammetry, and galvanostatic cycling, indicates for the solution high ionic conductivity and sodium transference number (t+), suitable stability window, very low electrode/electrolyte interphase resistance and sodium stripping/deposition overvoltage. Direct exposition to flame reveals the remarkable safety of the solution due to missing fire evolution under the adopted experimental setup. The solution is further investigated in sodium cells using various electrodes, i.e., mesocarbon microbeads (MCMBs), tin-carbon (Sn–C), and sulfur-multiwalled carbon nanotubes (S-MWCNTs). The results show suitable cycling performances, with stable reversible capacity ranging from 90 mAh g−1 for MCMB to 130 mAh g−1 for Sn–C, and to 250 mAh g−1 for S-MWCNTs, thus suggesting the electrolyte as promising candidate for application in sustainable sodium-ion and sodium-sulfur batteries.