Multi-scale structural description of siloxane–PPO hybrid ionic conductors doped by sodium salts

Abstract

Alkaline metal doped organic–inorganic hybrids have potential applications in the field of portable energy sources. Attractive sol–gel derived urea cross-linked polyether, siloxane–PPO (poly(propylene oxide)) hybrids doped with sodium salts (NaClO4 and NaBF4) were examined by multi-spectroscopic approach that includes complex impedance, X-ray powder diffraction (XRPD), small angle X-ray scattering (SAXS), 29Si and 23Na magic-angle spinning nuclear magnetic resonance (NMR/MAS), Na K-edge X-ray absorption near edge structure (XANES) and Raman spectroscopies. The goals of this work were to determine which cation coordinating site of the host matrix (ether oxygen atoms or carbonyl oxygen atoms) is active in each of the materials analyzed, its influence on the nanostructure of the samples and its relation with the thermal and electrical properties. The main conclusion derived from this study is that the NaBF4 salt has a much lower solubility in the hybrid matrix than the NaClO4 salt. Furthermore, the addition of a large amount of salt plays a major role in the hybrid nanostructure and electrical properties, modifying the PPO chain conformation, weakening or breaking the hydrogen bond of the polyether–urea associations and changing the polycondensation and aggregation processes involving the siloxane species.