Ion-conducting properties of SiO₂ gels containing lithium salt

Abstract

Impedance spectroscopy was employed to characterize the electrical properties of lithium acetate and lithium chloride-containing SiO₂ gels. Gels with various lithium salt contents were prepared by mixing TEOS (tetraethylorthosilicate), ethanol, water, lithium salt and the corresponding acid (hydrochloric or acetic acid). The conductivity of the gels was measured on heating from ambient temperature up to 230 °C under dynamic vacuum and again on cooling. The conductivity of the as-prepared wet gels is dominated by the electrolyte solution in the pores. On cooling, the gels exhibit Arrhenius behaviour and examination of the electrical modulus data reveals that each sample possesses two thermally activated processes. Comparison with impedance measurements made on polycrystalline pellets of lithium acetate dihydrate and lithium chloride indicates that the higher impedance process is associated with the lithium salt. As a physical origin for the better conducting process, it is suggested that conduction takes place along the surface of the pores connecting crystalline regions. The trend in conductivity with composition of the LiCl-containing gels is analogous with that of ceramic composite electrolytes such as Lil-Al₂O₃ and Lil-SiO₂.