Mechanical properties of PAN-based gel electrolytes: small-amplitude oscillatory shear study

Abstract

Polymer electrolytes with ionic conductivities on the order of mS cm^-1 at room temperature were prepared from the gelification of LiClO₄ /ethylene carbonate–propylene carbonate (EC–PC) solutions into a poly(acrylonitrile) (PAN) matrix. Oscillating rheological experiments were performed on gels prepared at different solvent/salt molar ratios in order to investigate their mechanical properties. Temperature sweep tests (25–120°C) showed changes in the rheological behaviour that was related to structural transitions. A strong–weak gel transition takes place at about 80°C, independent of salt concentration hence assignable only to the polymeric matrix. This transition is completely reversible during cooling ramps and represents a necessary mechanical property from a processing standpoint. A gel–sol transition was observed at ca. 110°C where both viscoelastic moduli reduce themselves by a factor 100, reporting the formation of a fluid system with G''>G'.