Design of alkaline metal ion conducting polymer electrolytes

Abstract

Abstract Polysiloxanes with covalently attached oligo ethylene oxide and di‐ t ‐butylphenol ( I ), naphthol ( II ), and hexafluoropropanol ( III ) were synthesized. The crosslinked polymers with a hexamethylene spacer were also prepared. The ion conductivities of the Li, Na, and K salts were measured as a function of temperature. The highest conductivities for K and Na of I at 30°C were 5.5 × 10 −5 and 5.0 × 10 −5 S/cm, respectively, when the ratio of the ion to ethylene oxide unit was 0.014. On the other hand, Li conductivity was 8.0 × 10 −6 S/cm when the ratio between Li and ethylene oxide unit was 0.019. The maximum conductivities of Li ions of II and III were in the order of 10 −6 and 10 −7 S/cm at 30°C, respectively. When the polymers were crosslinked by a hexamethylene residue, the ion conductivities decreased while the degree of crosslinking increased. The temperature dependence of the cation conductivities of these systems could be described by the Williams‐Landel‐Ferry (WLF) and the Vogel‐Tammann‐Fulcher (VTF) equation. The results demonstrate that ion movement in these polymers is correlated with the polymer segmental motion. The order of ionic conductivity was K + > Na + ≫ Li + . This suggests that steric hindrance and π‐electron delocalization of the anions attached to polymer backbone have a large effect on ion‐pair separation and their ionic conductivities. Thermogravimetric analysis of the polymers indicated that the degradation temperature for I and II were about 100°C higher than for poly(siloxane‐g‐ethylene oxide). This is due to the antioxidant properties of sterically hindered phenols and naphthols. © 1993 John Wiley & Sons, Inc.