A dielectric relaxation study of nanocomposite polymer electrolytes

Abstract

(PEO)4:LiClO4 and the effect of δ-Al2O3 nano-fillers on the polymer electrolyte have been investigated by differential scanning calorimetry (DSC) and dielectric relaxation studies. The DSC studies indicated a decrease in the glass transition temperature of (PEO)4:LiClO4 in the presence of fillers. The polymer–salt complex exhibited a conductivity of σD.C.=4.0×10−7Scm−1 at room temperature (298K). In the presence of 4wt% δ-Al2O3 fillers, the ionic conductivity increased by almost two orders of magnitude and exhibited a value of σD.C.=1.5×10−5Scm−1 (298K). By comparing the conductivity data with the calorimetric glass transition it is evident that the enhanced conductivity can be attributed to a speeding up of the segmental polymer dynamics. Hence, the combined data indicate a direct coupling between Li+ ion motions and polymer segmental dynamics, even when 4wt% nano-fillers have been introduced. From the temperature dependence of the conductivity relaxation time, which, thus, is coupled to the structural (α) relaxation time, it is understood that the fragility of the polymer electrolytes decreases with increasing filler concentration. The decrease in Tg and fragility suggests that the interaction between the nano-fillers and polymer is mainly non-attractive in nature. Moreover, the dielectric relaxation studies show that the β-relaxation speeds up with increasing concentration of filler particles. However, this speeding up is probably of less importance for the ionic conductivity. It was also found that the activation energy of the β-relaxation of PEO decreases in the presence of δ-Al2O3 nano-fillers and lithium salt. The strength of the β-relaxation increases also in the presence of salt ions. The γ-relaxation seems to be unaffected by the salt and fillers.