Ion association effects and ionic conductivity in polymer electrolytes

Ion association effects are essential for the understanding of ionic transport in polymer electrolytes. Ionic conductivity measurements on polyether-salt systems such as poly (propylene glycol), poly(ethylene oxide) and polyether modified poly-di-methyl-siloxanes complexed with triflate and perclorate salts have shown that plots of the molar conductivity versus the salt concentration have a characteristic shape. An aprotic polymer electrolyte behaves very much like a solution of a salt in a low permittivity aprotic solvent in which there are dissociated (“free”) ions, contact ion pairs and triplets present. The permittivity of the polymer electrolytes has been determined in order to calculate the fraction of free ions using an extended Denison-Ramsey equation. The enhancement of the ionic conductivity has earlier been suggested to be mainly due to either redissociation or the formation of triplets. This investigation supports redissociation.