Influence of PEG-borate ester as a Lewis acid on ionic conductivity of polymer electrolyte containing Mg-salt

We produced a novel Mg2+ conducting polymer electrolyte and added a poly(ethylene glycol) (PEG)-borate ester as a new type plasticizer having a Lewis acidity and investigated the influence of the Lewis acidity of the PEG-borate ester to a solid polymer electrolyte containing Mg(ClO4)(2) salt. Adding the PEG-borate ester into the electrolyte shows the increase in the ionic conductivity of the polymer electrolyte. By measuring the glass transition temperature (T-g) of the polymer electrolytes using differential scanning calorimetry, it became clear that the mobility of the carrier ion increases with increasing the amount of the PEG-borate ester. By investigating the temperature dependence of the ionic conductivity using William-Landel-Ferry type equation and measuring Raman spectra of the polymer electrolytes, it was found that the concentration of the carrier ion increases with increasing the amount of the PEG-borate ester in the polymer electrolyte. Furthermore, by estimating the transference number of the Mg2+ cation and performing the ab initio calculation for the PEG-borate ester, it is suggested that the PEG-borate ester may enhance the degree of dissociation of the Mg salt in the polymer electrolyte to increase the ratio of the free ion, especially Mg2+, by interacting with and trapping the ClO4- anion of the salt as a Lewis acid. (C) 2003 The Electrochemical Society.