Mechanism of Ionic Conductivity in Poly(ethyleneglycol 400)/(LiCl)x Electrolytic Complexes: Studies Based on Electrical Spectroscopy

This report describes the preparation of nine solvent-free (PEG400)/(LiCl) x complexes (0.00207 ≤ x ≤ 1.40665), together with a detailed investigation of their mechanisms of ion motion, carried out by impedance spectroscopy in the range from 20 Hz to 1 MHz. An accurate analysis of the real and imaginary components of their conductivities indicated that a full characterization of the AC electrical response for (PEG400)/(LiCl) x complexes requires an equivalent circuit analysis for frequencies lower than 1 kHz and a correlated ionic motion analysis based on a universal power law (UPL) for frequencies higher than 1 kHz. Ion−ion interactions in the (PEG400)/(LiCl) x systems were investigated by studying the equivalent conductivity profiles of the materials as a function of salt concentration and temperature. Results revealed the presence of two conductivity regions in (PEG400)/(LiCl) x materials, i.e., region I, detected at 0.0720 ≤ c 1/2 ≤ 0.6214 (mol/kg) 1/2, and region II, at c 1/2 ≥ 0.6214 (mol/kg) 1/2 . The conductivity mechanisms proposed in these two regions are regulated by two phenomena: intrachain hopping (intra-CH) of ions between coordination sites distributed along the polyethereal chains and interchain hopping (inter-CH) migration of ions. These events were demonstrated to depend on the segmental motion, the distribution of “free” Cl - ions along the PEG chains, and the site relaxation rate. This latter process takes place when a Li + ion hops “successfully” between two distinct polyethereal coordination sites. Finally, these materials show a conductivity of ca. 3.7 × 10 -5 Scm -1 at 25 °C.