On the origin of conductivity enhancement in polymer-ceramic composite electrolytes

This paper analyzes thermal history dependent conductivity data of a PEO:Li BF4-TiO2 (20 wt.%) electrolyte to understand the origin of conductivity enh ancement in polymer-ceramic composite electrolytes. The polymer-ceramic com posite electrolytes are proposed to comprise of an assemblage of molecular dipoles whose orientations are dependent upon temperature, prior thermal hi story, and electric field. One of the major factors contributing to the con ductivity is the orientation of these dipoles. Oriented dipoles augment con ductivity; however, thermal energy at higher temperatures tends to randomiz e their orientation. A specimen cooled rapidly from high temperature exhibi ts low conductivity, and if held isothermally its conductivity increases wi th time. The conductivity enhancement has been attributed to the ordering o f dipole moments. A reduction in conductivity as a function of time may als o be observed in these electrolytes, which is attributed to crystallization of the polymer phase. (C) 2001 Elsevier Science B.V. All rights reserved.