Modification of polymer electrolyte blend PEO/PVDF–HFP by low-energy O+ ion irradiation to improve electrolyte behavior

Abstract

PEO/PVDF–HFP [poly(ethylene oxide)/poly(vinylidene fluoride-co-hexafluoropropylene)] solid polymer electrolyte blend incorporating varying weights of LiTFSI [lithium bis (trifluoromethane) sulfonimide] salt was prepared. The blend with 20 wt.% of salt that exhibits maximum ionic conductivity was subjected to microstructural modification by exposing to low-energy ions of oxygen at different fluences. The ionic conductivity of the system increases by one order in magnitude when subjected to oxygen ion irradiation. The dielectric loss tangent curves are used to extract ions relaxation time. The relaxation time τ of the system is reduced from 1.42 to 0.71 μs upon irradiation which indicates enhanced segmental motion due to a rise in amorphous region in polymer matrix. The ion activation energy in the system decreases to 0.041 eV from 0.063 eV. Dielectric studies suggest an increase in dipoles in the irradiated systems possibly due to polymer chain scission in the matrix. The increase in disordered phase by ion irradiation is supported by change in crystallinity from 24% for the unirradiated systems to about 14% for the irradiated systems by X-ray diffraction and differential scanning calorimetry analysis. The shift in prominent peaks observed in Fourier transform infrared spectroscopy suggests possible scission of the polymer chains.