Sodium ion conducting gel polymer electrolyte using poly(vinylidene fluoride hexafluoropropylene)

Highlights: • PVdF-HFP gel polymer electrolyte film (30–50 µm of thickness) is introduced. • Good ionic conductivity of 1–2 mS.cm⁻¹ is obtained at room temperature. • Stable specific capacity of 100 mAh.g⁻¹ for Na_0.44MnO₂ using GPEs at C/10, 25 °C. -- Abstract: Gel polymer electrolyte (GPE) films using polyvinylidene fluoride – hexafluoropropylene (PVdF – HFP) matrix were prepared for aim to achieve good sodium-ion conductivity at room temperature. GPE of PVF-HFP were formed by microporous PVDF-HFP membranes filled and swollen in different liquid electrolytes: GPEs were formed by microporous PVDF-HFP membranes filled and swollen in different liquid electrolytes: NaClO₄, NaPF₆ and NaTFSI salts dissolved in mixtures of carbonate solvents (propylene carbonate (PC), fluoroethylenecarbonate (FEC)) or ionic liquids (1-ethyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide and 1-butyl-3-methyl bis(trifluoromethanesulfonyl)imide). The effect of different electrolytes on the structure and morphology, electrolyte absorption and sodium ionic conductivity of activated membrane were investigated. GPEs showed "sponge-like" structure with high porosity of 80–85% and large pore size. The ionic conductivity of GPEs reached 1–2 mS.cm⁻¹ at room temperature. Sodium intercalation into Na_0.44MnO₂ electrode was performed in coin-cell type by using GPEs as conduction media. Cycling data of sodium cell using PVdF-HFP/NaClO₄ 1 M-PC:2%FEC exhibited an excellent stable specific capacity of 100 mAh.g⁻¹ at room temperature.