Ion−Oligomer Interactions in Poly(ethylene glycol)400/(LiCl)x Electrolyte Complexes

By reacting metallic lithium with 1-chlorobutane we obtained a very anhydrous LiCl that allowed us to prepare 10 poly(ethylene glycol)/(LiCl)x complexes (0≤ x ≤ 1.40665) using a reaction protocol that does not require added solvents. The interactions between Li+ and Cl-ions and poly(ethylene glycol) (PEG) ligands in the polymer electrolytes were investigated by mid and far FT-IR spectroscopy. Results revealed that (a) the PEG chains assume a TGT type conformation; (b) Li+ ions are coordinated by ethereal oxygens of the PEG ligand; (c) at an Li/O molar ratio less than 0.036, Cl- ions form hydrogen bonding cages with the terminal OH groups of PEG chains; (d) at an Li/O molar ratio greater than 0.036, Cl- ions are present both in hydrogen bonds and as “free anions” along PEG chains. Conductivity measurements made at different temperatures showed that these systems conduct ionically, with two distinct conductivity regions detected. The possible correlation between the conductivity and the structure of these electrolytic systems was also investigated showing that the “free ionic carriers”, which are responsible for the Aσ values, are directly related to the total “free anion” concentration. The conductivity of PEG 400/(LiCl)0.349 is on the order of about 1 × 10-4 S cm-1 at 25 °C.