SOLUBILITY OF INORGANIC SALTS IN POLY(ETHYLENE OXIDE) AND EFFECTS OF POLY(ETHYLENE OXIDE) MOLECULAR-WEIGHT AND SALT SPECIES ON THE IONIC-CONDUCTIVITY

A series of inorganic salts was dissolved in poly(ethylene oxide) (PEO) with average molecular weight of 200 approximately 6000 to determine their solubility. The solubility of lithium salts in PEO decreased with the increase of PEO molecular weight. The terminal hydroxyl group was revealed to be much more effective to increase solubility of the added salts than ether oxygen. Sodium salts showed PEO molecular weight dependence on the solubility similar to that for the lithium salts. Little molecular weight dependence of PEO was however found in the solubility of potassium salts. From a structural analogy between water molecule and the hydroxyl group, solubility order among inorganic salts in PEO was expected to be similar to those in water, but no relation was found. The maximum ionic conductivity for PEO (molecular weight: 200)/LiClO4 system was found at [LiClO4] = 1.0 mol/l. This was demonstrated to be attributed to the matrix viscosity. Higher ionic conductivity was observed in the PEO systems containing 0.3 mol/l salt with larger cation radius and those with lower lattice energy.