Triglyme-based solvate ionic liquid gelled in a polymer: A novel electrolyte composition for sodium ion battery

We report studies on a novel gel polymer electrolyte (GPE) based on solvate ionic liquids (SILs) comprising complex cation [Na-(glyme)]+ and anion ClO4- for battery application. SILs are prepared by varying NaClO4 in triglyme (G3), immobilized in poly(vinylidene-fluoride-co-hexafluoropropylene) to yield SIL-GPEs as free-standing, flexible films. The morphology/structural and salt-glyme-polymer interactions in SIL-GPEs are studied from SEM, X-ray diffraction, FTIR/Raman and TG analyses. Electrochemical investigations suggest a high ionic conductivity (~2.54 ×10−3 S cm−1), a high Na-ion transport number (~0.73) and wide electrochemical stability window (~4.7 V) for an optimum composition comprising 0.3:1 molar ratio of NaClO4 and G3. Suitability of the SIL-GPE is tested in quasi-solid-state sodium-ion battery by fabricating half-cell with ball-milled V2O5 as the positive electrode. The cell offers a maximum capacity of ~111 mA h g−1 in first cycle at a current rate of 0.05 C, and sustains ~55 mA h g−1 after 65 charge-discharge cycles at 0.1 C.