Physical Characterization of Ionic Liquid-Modified Polyvinyl Alcohol and Sodium Thiocyanate Polymer Electrolytes for Electrochemical Double-Layer Capacitor Application

Novel gel polymer electrolytes(GPEs)composed of polyvinyl alcohol(PVA)and sodium thiocyanate were developed via a solution casting technique.An ionic liquid(IL),1-ethyl-3-methyl-imidazolium tricyanomethanide([EMIM][TCM]),was doped into a polymer–salt complex system(PVA+NaSCN)to further enhance the conductivity.IL-doped polymer electrolyte(ILDPE)films were characterized using X-ray diffraction(XRD),polarized optical microscopy(POM),Fourier-transform infrared(FTIR)spectroscopy,and conductivity measurements.XRD was performed to check the degree of crystallinity and amorphicity of the ILDPE films,and the amorphicity of GPEs increased with the increase of the IL content.POM was employed to evaluate the changes in the surface morphology due to the inclusion of salt and IL in the PVA.The compositional nature of the GPE films was examined via FTIR studies.The electrical and electrochemical properties were characterized by cyclic voltammetry and electrochemical impedance spectroscopy.The maximum conductivity for the GPE film was estimated to be 1.10×10^(-5) S/cm for 6%(mass fraction)of IL in the polymer–salt complex.The ionic transference number was approximately 0.97.An electrochemical double-layer capacitor(EDLC)was built from optimized GPE films and reduced graphene oxide-based electrodes.The specific capacitance calculated from the cyclic voltammograms of the EDLC cells was 3 F/g.