Phase relations and conductivity in the system poly(ethylene oxide)LiClO 4

Abstract

DSC, DTA, TGA, X-ray, and conductivity measurements have been carried out on mixtures of purified poly(ethylene oxide) (PEO) and lithium perchlorate and the phase diagram of the system PEO + LiClO 4 has been determined. The mixtures showed pronounced thermal decomposition beginning at 100 – 150 °C (depending on LiClO 4 content) so that phase equilibria could not be determined above the decomposition temperature. The phase diagram indicates the presence of three compounds containing, respectively, one, two, and three Li ions per —CH 2CH 2O— repeating unit. Glass transition temperatures T g increased with increasing lithium content from 213 K for pure PEO to 269 K at n = 2. Conductivities went through maxima at n = 12 reaching 2.5 × 10 −3 S cm −1 at 373 K. The temperature dependence of conductivity could be represented by the Vogel—Tammann—Fulcher (VTF) equation over the whole temperature range in which the mixtures are amorphous, 298 – 393 K ( n = 4, 8), above 313 K ( n = 12) or above 323 K ( n = 16).