Investigation of the Effect of Lewis Acid on Ionic Conductivity of Polymer Electrolyte Containing Mg Salt

In order to investigate the influence of Lewis acidity on the ionic conductivity of poly(ethylene glycol) (PEG) poly(ethylene oxide) (PEO)-type polymer electrolyte, we designed a new solid polymer electrolyte based on salt complexs of PEO chains cross-linked by a boric acid group as a Lewis acid. To change the concentration of the Lewis acid point in the polymer electrolyte, the length of the PEO repeating unit was controlled. The ionic conductivity of the polymer electrolyte increased with increasing the length of the PEO chain and with decreasing the concentration of the cross-linking point by the boric acid group. By measuring the glass transition temperature of the polymer electrolytes using differential scanning calorimetry, it was found that the increases with decreasing the concentration of the cross-linking point. By investigating the temperature dependence of the ionic conductivity using William-Landel-Ferry-type equation and measuring Raman spectra of the polymer electrolytes, it became clear that the concentration of the carrier ion in the polymer electrolyte increased with increasing the concentration of the Lewis acid point by the boric acid group. Furthermore, the transference number of the cation increased with increasing the concentration of the boric acid group. By the ab initio calculation for the PEG-borate ester as a model molecule to investigate on the Lewis acidity of boric acid group, it was supported that the boric acid group may act as a Lewis acid to enhance the solubility of the salt in the polymer electrolyte by interacting with and trapping the anion of the salt. © 2003 The Electrochemical Society. All rights reserved.