Role of plasticizerʹs dielectric constant on conductivity modification of PEO–NH4F polymer electrolytes

The addition of plasticizer to the polyethylene oxide (PEO)–ammonium fluoride (NH4F) polymer electrolytes has been found to result in an increase in conductivity value and the magnitude of increase has been found to depend upon the dielectric constant of the plasticizer used. The addition of dimethylacetamide as a plasticizer with dielectric constant (ϵ=37.8) higher than that of PEO (ϵ∼5) results in an increase of conductivity by more than three orders of magnitude whereas the addition of diethylcarbonate as a plasticizer with dielectric constant (ϵ=2.82) lower than that of PEO does not enhance the conductivity of PEO–NH4F polymer electrolytes. The increase in conductivity has further been found to depend upon the concentration of plasticizer, the concentration of salt in the polymer electrolyte as well as on the dielectric constant value of the plasticizer used. The conductivity modification with the addition of plasticizer has been explained on the basis of dissociation of ion aggregates formed in PEO–NH4F polymer electrolytes at higher salt concentrations.