Charge carrier dynamics and relaxation in highly conducting gel polymer electrolytes added with adiponitrile and dual redox

Abstract

The fundamental understanding of the relationship between ion transport and segmental dynamics of polymer chains in polymer electrolytes is crucial for achieving high ionic conductivity at room temperature for technological applications in supercapacitors, batteries, etc. In this work, the ion dynamics and relaxation have been studied for gel polymer electrolytes (GPEs) containing P(VdF-HFP) as host polymer, adiponitrile as a plasticizer, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as ionic liquid, and diphenylamine and copper iodide redox additives as fillers. The crystallization temperature of the ionic liquid and the melting temperature of the plasticizer play important roles in ion dynamics. The highest room-temperature ionic conductivity (3.3 × 10−3 S/cm) was obtained for the GPE filled with dual redox additives. The broadband ac conductivity spectra have been analyzed by using the Universal Power law model coupled with the Poisson–Nernst–Planck (PNP) model. The solid–solid phase transition of the ionic liquid affects the grain and grain boundary regions of the GPEs due to the presence of redox fillers. The temperature dependence of the dielectric spectra of the GPEs containing redox fillers confirms the phase transition at the crystallization temperature. The electric modulus and dielectric spectra have been analyzed by using the Havrilliak–Nigami, Kohlrausch–Williams–Watts, and derivative dielectric constant functions. The scaling of ac conductivity and modulus spectra confirms a common ion conduction and relaxation mechanism for the GPEs. The influence of dual redox additives is clearly observed in the values of ionic conductivity, ion diffusivity, and relaxation time.