Property-Relaxation Correlations in 3D-Siloxane/Polyether Hybrid Polymer Electrolytes

The thermomechanical and transport properties of a series of hybrid polymer electrolytes are examined by means of differential scanning calorimetry, rheological analysis and broadband electric spectroscopy. The electrolytes are composed of 3D-oligosiloxane defect clusters grafted with polyether chains and doped with LiClO4, with concentration ranging from 0 to 1.4 mol·kg-1. The thermomechanical properties are mainly modulated by the balance of interactions taking place within the polyether domains. The materials show low Tg and no crystallization in a wide salt concentration range, while the mechanical modulus, between 104 and 105 Pa, is stable up to at least 100 °C. A detailed electric characterization, combined with the results from vibrational spectroscopy analysis, elucidates the factors influencing the transport properties. The conductivity reaches 8 × 10-5 S·cm-1 at 30 °C for intermediate salt concentrations. The sluggishness of the host matrix appears to be the limiting factor depressing the conductivity at higher salt concentrations. Conversely, the appearance of ion aggregates plays a negligible role, at least in the concentration range examined.