Ionic conductivity of polymer electrolytes based on phosphate and polyether copolymers

Abstract

Linear polyphosphate random copolymers (LPC) composed of phosphate as a linking agent with poly(ethylene glycol) (PEG) and/or poly(tetramethylene glycol) (PTMG) were synthesized to increase local segmental motion for improved ion transport. Ionic conductivity and thermal behavior of LPC series-LiCF3SO3 complexes were investigated with various compositions, salt concentrations and temperatures. The PEG(70)/PTMG(30)/LiCF3SO3 electrolyte exhibited ionic conductivity of 8.04 x 10(-5) S/cm at 25 degrees C. Salt concentration with the highest ionic conductivity was considerably dependent on EO/TMO compositions in LPC series-salt systems. Relationship between solvating ability and chain flexibility with various compositions and salt concentrations was investigated through theoretical aspects of the Adam-Gibbs configurational entropy model. Temperature dependence on the ionic conductivity in LPC6 series-salt systems suggested the ion conduction follows the Williams-Landel-Ferry (WLF) mechanism, which is confirmed by Vogel-Tamman-Fulcher (VTF) plots. The ionic conductivity was affected by segmental motion of the polymer matrix. VTF parameters and apparent activation energy were evaluated by a non-linear least square minimization method. These results suggested that the solvating ability of the host polymer might be a dominant factor to improve the ionic conductivity rather than chain mobility. (C) 1999 Published by Elsevier Science B.V. All rights reserved.