Ionic conductivity and relaxation studies in PVDF-HFP:PMMA-based gel polymer blend electrolyte with LiClO4 salt

Abstract

Poly(vinylidene fluoride-hexafluropropylene) (PVDF-HFP) and poly(methyl methacrylate) (PMMA)-based gel polymer electrolytes (GPEs) comprising propylene carbonate and diethyl carbonate mixed plasticizer with variation of lithium perchlorate (LiClO4) salt concentrations have been prepared using a solvent casting technique. Structural characterization has been carried out using XRD wherein diffraction pattern reveals the amorphous nature of sample up to 7.5wt.% salt and complexation of polymers and salt have been studied by FTIR analysis. Surface morphology of the samples has been studied using scanning electron microscope. Electrochemical impedance spectroscopy in the temperature range 303–363K has been carried out for electrical conductivity. The maximum room temperature conductivity of 2.83×10−4S cm−1 has been observed for the GPE incorporating 7.5wt.% LiClO4. The temperature dependence of ionic conductivity obeys the Arrhenius relation. The increase in ionic conductivity with change in temperatures and salt content is observed. Transport number measurement is carried out by Wagner’s DC polarization method. Loss tangent (tan δ) and imaginary part of modulus (M′′) corresponding to dielectric relaxation and conductivity relaxation respectively show faster relaxation process with increasing salt content up to optimum value of 7.5wt.% LiClO4. The modulus (M′′) shows that the conductivity relaxation is of non-Debye type (broader than Debye peak).

Keywords

• Gel polymer electrolyte
• ionic conductivity
• transport number
• Wagner’s DC polarization
• impedance