Ionic properties of non-aqueous liquid and PVDF-based gel electrolytes containing a cesium thiolate/disulfide redox couple

Abstract

Liquid electrolytes containing a cesium thiolate/disulfide redox couple, prepared from 5-mercapto-1-methyltetrazole cesium salt (CsT) and di-5-(1-methyltetrazole)disulfide (T 2) dissolved in several aprotic solvents and solvent mixtures, have been studied using various techniques. FTIR spectroscopy reveals that relatively strong interactions occur between the reduced species T − and DMSO or DMF while Cs + ions are very weakly coordinated to the SO or CO bond. It is shown that the electrolyte consisting of 1.55 mol kg −1 CsT in the solvent mixture DMSO/DMF (40/60%) exhibits the highest conductivity (1.1×10 −2 and 2.3×10 −2 S cm −1 at 23 and 80 °C, respectively), and that the presence of the oxidized species T 2 does not affect significantly its electrical properties up to a CsT:T 2 molar ratio of 5:1. Conductivity values as a function of salt concentration are discussed in terms of the effective number of charge carriers, taking into account the level of ionic association, and of the ionic mobility. Optically transparent gel electrolytes have been prepared by incorporation of the optimal liquid electrolyte into various amounts of poly(vinylidene fluoride) (PVDF). It is shown that ionic mobility is not much affected by the polymer concentration, suggesting that migration of ions occurs mainly through the solvent mixture surrounded by the PVDF matrix.