Diglyme-Based “Solvate Ionic Liquid” Gelled in Poly(vinylidine fluoride-co-hexafluoropropylene): A Flexible Electrolyte for High-Performance Magnesium-Ion Batteries

Owing to their appealing electrochemistry, high electrochemical stability, excellent transport characteristics, low volatility, and high safety, glyme-based electrolytes are receiving wide attention in rechargeable batteries and other energy storage systems. Herein, we report a free-standing and flexible film of magnesium-ion conducting gel polymer electrolyte comprising diglyme (G2) incorporated with a Mg-salt [Mg(ClO 4 ) 2 ] referred to as a “solvate ionic liquid (SIL)”, immobilized in a host polymer [poly(vinylidene fluoride- co -hexafluoropropylene) (PVdF-HFP)]. Structural changes in PVdF-HFP upon incorporation of G2 and Mg-salt have been studied via X-ray diffraction, whereas conformational changes and ion–glyme–polymer interactions have been investigated by using Fourier transform infrared spectroscopy and Raman studies. The wide electrochemical stability window (∼4.3 V vs Mg/Mg 2+ ), high room-temperature ionic conductivity (∼3.15 × 10 –3 S cm –1 ), significant Mg 2+ transport number ( t Mg 2+ ∼0.49), and thermal stability up to 100 °C are attractive properties of the glyme (G2)-based GPE films for application in Mg batteries of possible flexible configuration. The Mg-MWCNT nanocomposite shows superior performance as an anode compared to pure Mg when interfaced with the GPE film as indicated from Mg-stripping/plating for long-term cyclic performance with low and stable polarization limited to ±250 mV at the constant current of 0.5 mA cm –2 . Further, the GPE shows excellent interfacial stability with the Mg-MWCNT nanocomposite electrode as evident from long-term electrochemical impedance spectroscopic studies. Studies indicate prospects of glyme-based GPEs, a class of electrolytes/separators, in high-voltage and hence high-energy-density flexible Mg-ion storage devices.