Solid polymer electrolytes based on polyethylene oxide and lithium trifluoro- methane sulfonate (PEO–LiCF 3SO 3): Ionic conductivity and dielectric relaxation

Abstract

Polymer electrolytes consisting of polyethylene oxide (PEO) and LiCF 3SO 3 were synthesized by solution casting method as a function of EO/Li ratio. An increase in the glass transition temperature of the polymer electrolytes with increasing Li salt content suggested the coordination of the Li ions to the oxygen atoms of polymer backbone. Dielectric spectroscopic studies were performed to understand the ion transport process in polymer electrolytes. The dc conductivity showed a maximum for EO/Li ≈ 24. The ac conductivity analysis revealed the existence of nearly constant loss (NCL) contribution at lower temperatures. The dielectric loss spectra showed the presence of one relaxation for all compositions, which is associated with the motions of the Li ion coordinated polymer segments. The relaxation has been characterized by the empirical Havriliak–Negami (H–N) equation. The temperature dependence of the relaxation times and the conductivity followed the Vogel–Tamman–Fulcher (VTF) equation yielding qualitatively similar pseudoactivation energies, which suggested strong coupling between the ionic conductivity and the segmental relaxation in the polymer electrolytes.