Ion Transport Properties of Some Mixed Halide Based Oxide Dispersed Composite Electrolyte Systems

Abstract

Composite solid electrolytes are a one class of electrolytes. The primary concern of these electrolytes is ionic conductivity ( ) s based on various transport characteristics. Though the alkali halides are intrinsic ionic conductors, they rarely meet the technological demands due to the limitation in their FRQGXFWLYLWLHV W\SLFDOO\ IRU .–$J,a -1cm-1 at 150o& .–&X%Ua -1cm-1 at 480o& .-CuI~9.0× 10-2 -1cm-1 at 450oC etc.). Therefore there was a genuine need to synthesize / tailor-make solid electrolytes which can have high conductivities. This could be realized by making the composite electrolytes with insulating oxide dispersions. Although the idea of composite electrolytes and thereby enhancing the ionic conductivity was proposed as early as 1973 when Liang [76] reported a 50 time increase for the LiI+Al2O3 system. Since then a large number of systems were developed and investigated for a search of higher and higher conductivities. A reasonably large number of studies on oxide dispersed metallic halides and alkali halides were conducted and reported by various researchers across the world. All these works were essentially targeted to develop electrolytes for the power sources for various applications such as cell phones, pagers, computers, light shutters, smart windows etc. The ever-increasing demand of power sources for modern electronic devices strongly motivate researchers to develop and investigate newer and newer electrolytes, which are the key components of power source / solid state battery. In view of the above requirements, the solid electrolyte preparation and their physical and electrical characterizations were carried out in the present thesis. In order to demonstrate the superiority of mixed matrix base for the oxide dispersion as compared to the case of single halide matrix and the resulting oxide dispersion characteristics-both in single and mixed matrices, a number of electrolytes in the following systems were prepared: (i) (KCl)1– x+(ZrO2)x; (ii) [(KCl)1– x + (NaCl)x]1–y+(ZrO2)y; (iii) [(KCl)1– x +(CuCl)x]1–y + (SnO2)y; (iv) [(BaCl2)1– x+(KCl)x]1–y + (ZrO2)y and (v) [(KCl)1–x+(KI)x]1–y+(ZrO2)y. These mixed systems were chosen to address the issues of the characteristics of oxides dispersed in mixed matrices in relation to that of single matrix composite electrolytes. In the systems (ii) and (iii), the essential charge carriers are cations, whereas, in systems (iv) and (v), the conduction is executed essentially by anions. The reason for choosing the KCl-based matrix is due to the fact that it does not undergo phase transformation before melting, thereby accommodating the effect of wide variation of temperature on transport characteristics to develop an empirical relationship of conductivity ( ) s and ionic mobility ( ) m with temperature. In a majority of the present studies, the dispersoid taken is ZrO2 particles (size ~1mm). This is due to the fact that in general, alumina is used as dispersoid for which systems were well studied and reported by other researchers. However, to the best of author’s knowledge, no systematic studies on ZrO2- dispersed composite electrolytes are reported in the literature.