Impact of Introducing EMIM-BF₄ as Ionic Liquid Solvent on Electrochemical Properties of PVdF–HFP Based Sodium Ion Conducting Gel Polymer Electrolytes

Depletion of lithium resources has forced scientists to search for alternative energy storage chemistries. Gel polymer electrolytes (GPEs) are being explored as an important option due to their leakage-free and superior electrochemical performance. The present work is focused on examining the impact of adding ionic liquid EMIM-BF₄ (1-ethyl-3-methylimidazolium tetrafluoroborate) on the electrochemical behavior of sodium-ion conducting GPEs containing ethylene carbonate and polypropylene carbonate solvents, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) polymer, and sodium tetrafluoroborate (NaBF₄) salt. The electrochemical behavior of the prepared GPEs is studied by complex impedance spectroscopy and other electrochemical studies. With the accumulation of 10 wt.% of EMIM-BF₄, the ionic conductivity is greatest, and increases from ~1.94 × 10⁻³ S cm⁻¹ to a maximum of ~7.98 × 10⁻³ S cm⁻¹ at room temperature. The electrochemical stability window (ESW) of the GPE is ∼ 4 V. To study the structural modification in electrolytes, Fourier transform infrared (FTIR) spectroscopy and x-ray diffraction (XRD) are conducted. The real and imaginary parts of permittivity and modulus behavior over a wide frequency range are also investigated and described.