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 less than or equal to x less than or equal to 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 bower 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 less than or equal to c1/2 less than or equal to 0.6214 (mol/kg)1/2, and region II, at c1/2 greater than or equal to 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 Lif ion hops "successfully" between two distinct polyethereal coordination sites. Finally, these materials show a conductivity of ca. 3.7 x 10-5 S/cm at 25°C.