In the present work, copolymer of poly(vinyl acetate-co-acrylonitrile), (poly(VAc-co-AN)) was produced and then converted to of poly(vinyl alcohol-co-acylonitrile), (poly(VA-co-CN)) via hydroysis. The polymer electrolytes on the basis of poly (ethylene oxide) (PEO)/poly(vinyl alcohol-co-acrylonitrile) (poly(VA-co-AN)) were produced and they were doped with certain fractions of 1-ethyl-3-methylimidazolium (IL)/lithium tetrafluoroborate (LiBF4). The production of a copolymer was justified by H-1-NMR and the structure of blend polymer electrolytes elucidated with Fourier-transform infrared spectroscopy (FT-IR) spectroscopy. Thermal measurements showed that all the electrolytes are almost stable up to 200 degrees C. Differential scanning calorimetry (DSC) results demonstrated the semicrystalline character of the electrolytes. The surface morphology was studied by scanning electron microscopy (SEM) confirmed the homogeneity of the electrolytes. The ionic conductivity was systematically studied with respect to temperature as well as the content of the polymer electrolytes. In dry state, poly(VA-co-AN) (PEO-20%IL-20/1LiBF(4)), S5 exhibited a conductivity of 2x10(-4)S/cm at RT and 7x10(-3)S/cm at 100 degrees C. Galvanostatic charge/discharge graph indicated good electrochemical reversibility up to 1000cycle with almost no loss in coulombic efficiency. A symmetrical cell comprising poly(VA-co-AN)/IL, S5 sample yielded a specific capacitance of 80Fg(-1) at 1A/g. The same electrolyte yielded a maximum energy density in supercapacitor as 61Whkg(-1) at a power density of 500Wkg(-1).