FTIR spectroscopic study and thermal and electrical properties of polymer electrolytes containing a cesium thiolate/disulfide redox couple

Abstract

High molecular weight (HMW) PEO-based copolymer (modified PEO) complexed with a cesium thiolate/disulfide redox couple, prepared from 5-mercapto-1-methyltetrazole cesium salt (CsT) and di-5-(1-methyltetrazole) disulfide (T 2), has been studied using various techniques. Phase diagrams of the modified PEO x –CsT and modified PEO x –CsT/0.1T 2 systems, developed using polarized light optical microscopy and differential scanning calorimetry, are discussed. It is shown that an intermediate compound and an eutectic of composition corresponding to a (CH 2–CH 2–O)/Cs molar ratio (O/Cs) of 12/1, which melts at 29°C, are formed. At high salt concentration (O/Cs≤8/1), non-spherulitic crystallites observed over the homogeneous amorphous phase are attributed to undissolved CsT. Ionic conductivity measurements show that the polymer electrolytes investigated in this work exhibit a conductivity maximum that occurs at the eutectic composition. Conductivity values as a function of salt concentration are discussed in terms of the effective number of charge carriers and of the stiffening of the polymer chains. The valuable role of the disulfide (T 2) for increasing the electrolyte conductivity is reported. The slight higher conductivity of the fully amorphous electrolyte containing CsT instead of KT may be correlated to the lower polyether–Cs + interaction, as revealed by FTIR spectroscopy.