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

This paper analyzes thermal history dependent conductivity data of a PEO:LiBF4-TiO2 (20 wt.%) electrolyte to understand the origin of conductivity enhancement in polymer-ceramic composite electrolytes. The polymer-ceramic composite electrolytes are proposed to comprise of an assemblage of molecular dipoles whose orientations are dependent upon temperature, prior thermal history, and electric field. One of the major factors contributing to the conductivity is the orientation of these dipoles. Oriented dipoles augment conductivity; however, thermal energy at higher temperatures tends to randomize their orientation. A specimen cooled rapidly from high temperature exhibits low conductivity, and if held isothermally its conductivity increases with time. The conductivity enhancement has been attributed to the ordering of dipole moments. A reduction in conductivity as a function of time may also be observed in these electrolytes, which is attributed to crystallization of the polymer phase. (C) 2001 Elsevier Science B.V. All rights reserved.