Impact of ionic liquid incorporation on ionic transport and dielectric properties of PEO-lithium salt-based quasi-solid-state electrolytes: role of ion-pairing

The present paper reports the preparation and characterization of ionic liquid immobilized quasi-solid-state electrolytes (QS-SEs) “PEO-LiPF6-ionic liquid (IL)” with polymer PEO, dopant salt (LiPF6) and ionic liquid, BMIMPF6 having common anion (PF6-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{PF}}_{6}^{ - }$$\end{document}). AC impedance and Raman spectroscopic measurements showed that ionic conductivity (σ) of QS-SEs increases with IL-content and partly controlled by number of free mobile ions and their mobility/polymeric chain flexibility. Differential scanning calorimetry (DSC) results showed that melting temperature (Tm), glass transition temperature (Tg) and degree of crystallinity (Xc) of QS-SEs decreases with IL-content due to the plasticization effect of added IL(BMIMPF6). Furthermore, the composition-dependent conductivity data with IL-concentration is discussed in terms of increasing amorphicity (or deceasing crystallinity) as well as ion-polymer and ion-ion interactions. Ion dynamics of QS-SEs is examined by converting the impedance data into different ionic transport formalisms like ionic mobility (μ), charge carrier density (N) using the loss tangent (tan δ) spectra and showing that amount of added IL/salt are the responsible factors for controlling overall ion transport mechanism.