The effect of [EMIm]BF4/Li+ Ionic liquid on PEO-based solid polymer electrolyte membranes characteristics as lithium-ion batteries separator

Abstract

Lithium-ion batteries have liquid electrolytes, which are corrosive and volatile, that would cause leakage and explosion during the rechargeable process at high temperatures. To overcome this problem, it is necessary to change the liquid electrolyte into a solid one, namely a solid polymer electrolyte. This work has prepared the solidpolymer electrolyte membranes by casting various 1-ethyl-3-tetrafluoroborate, [EMIm]BF4/Li+ ionic liquid, and PEO. In this study, [EMIm]BF4/Li+, a Li+ ion-attached ionic liquid, has been synthesized using a simple metathesis reaction between 1-ethyl-3- methylimidazolium-bromide, [EMIm]Br, and lithium tetrafluoroborate, LiBF4 salt. [EMIm]Br has been synthesized from 1- methylimidazole and bromoethane precursors using Microwave Assisted Organic Synthesis (MAOS) method. The functional groups and structures of [EMIm]Br and [EMIm]BF4/Li+ have been confirmed by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectra analysis. The analysis of ionic conductivities, crystallinities, mechanical properties, surface morphologies, and thermal stabilities have been confirmed by using Electrochemical Impedance Spectroscopy (EIS), X-ray Diffraction (XRD), and tensile tester, Scanning Electron Microscopy (SEM), and Thermogravimetry Analysis (TGA), respectively. The highest ionic conductivity is 1.83 x 10-3 S.cm-1 at room temperature for polymer electrolyte membrane with 16% weight of the [EMIm]BF4/Li+ ionic liquid and also exhibits good mechanical flexibility and thermal stability.