Effect of organic solvent addition on electrochemical properties of ionic liquid based Na+ conducting gel electrolytes

A novel sodium ion conducting gel polymer electrolyte comprising room temperature ionic liquid, 1-ethyl 3 methyl imidazolium trifluoro-methane sulfonate (EMIT incorporated with ethylene carbonate and propylene carbonate and its solution with sodium trifluoromethane sulfonate (NaTf) entrapped in poly(vinylidinefluorideco-hexfluoropropylene) (PVdF-HFP) is prepared using solution cast technique. The gel electrolyte is obtained in the form of free-standing transparent film. The gel electrolyte offers electrical conductivity of similar to 10(-3) S cm(-1) at - 30 degrees C with good mechanical, thermal and electrochemical stability window. The electrical conductivity is measured as a function of temperature and found to be consistent with Vogel-Tamman-Fulcher (VTF) relationship in the temperature range from 30 degrees C to 75 degrees C. Sodium ion conduction in the gel electrolyte film is confirmed from cyclic voltammetry and transport number measurements. The value of the sodium ion transport number of the ionic liquid based gel electrolyte is similar to 0.19. The sodium sulfur battery with the gel electrolytes delivers the first discharge capacity of 267 mAh g(-1) sulfur and then it decreases with repeated charge-discharge cycles.