Charge Carrier Relaxation in Different Plasticized PEO/PVDF-HFP Blend Solid Polymer Electrolytes.

In this article, we report first the effect of concentration of ethylene carbonate plasticizer on conduction and relaxation of charge carriers in PEO/PVDF-HFP-LiClO4 blend electrolytes. Second, the results for different plasticizers, such as ethylene carbonate, propylene carbonate, and dimethyle carbonate, on the conductivity and relaxation in these blend electrolytes are compared. We have followed a new approach for the analysis of the conductivity data. The frequency dependent conductivity is analyzed using random free-energy barrier model, taking into consideration the low frequency polarization effect. The temperature dependences of the ionic conductivity and the relaxation time obtained from the model exhibit Vogel-Tammann-Fulcher behavior. Using the scaling of the ac conductivity spectra it is observed that the relaxation dynamics of charge carriers in blend electrolytes are independent of temperature but depend on the nature of plasticizers. The electric modulus is studied using Havriliak-Negami function for the understanding of ionic relaxation. The modulus data are also analyzed using nonexponential Kohlrausch-Williams-Watts function. The temperature dependence of the relaxation time obtained from modulus analysis follows Vogel-Tammann-Fulcher relation for all plasticized electrolytes. It is observed that the stretched exponent is much lower than unity, which suggests that charge carrier relaxation is highly nonexponential in these plasticized electrolytes.