Study of correlations between microstructure and conductivity in a thermoplastic polyurethane electrolyte

Abstract

Micro-Raman and positron annihilation lifetime spectroscopy (PALS) have been used to investigate the structure of a thermoplastic polyurethane/LiClO4 solid flexible polymer electrolyte at room temperature. Correlation between the free volume and carrier concentration with ionic conductivity was observed. The polyurethane soft phase consisted of a poly(tetramethylene glycol-co-ethylene glycol) copolymer reinforced by condensation with hexamethyldiisocianate. The range of salt concentration between 5 and 35 wt percent, which attained the beginning of phase segregation, was also studied by differential scanning calorimetry (DSC), which showed the presence of three thermal events; the soft-phase Tg, a change in heat capacity suggested as the hard-phase Tg, and a hard-phase ordering endotherm. The total ionic conductivity was found to be approximately 4 x 10-6 S cm-1 at 23 oC up to 27 wt percent salt, whereas there were pronounced changes observed by the spectroscopic techniques.