Effect of clay-based amorphous silica on structural and electrical properties of LISICON-type ceramic electrolytes, Li4SiO4

Abstract

LISICON-type materials are an important class of solid-state electrolytes due to their high ionic conductivity along with decent chemical and electrochemical stability. In this study, Li₄SiO₄ using synthetic silica and amorphous silica extracted from halloysite clay were synthesized by sol gel method. X-ray diffraction analysis revealed the crystal phase, structure, and unit cell parameters of each electrolyte. Additionally, laser particle sizing determined the distribution of particle sizes, while energy-dispersive X-ray spectroscopy confirmed the elemental composition of both materials. Complex impedance spectroscopy, conducted between 10 and 10⁷ Hz at temperatures ranging from room temperature to 500°C, assessed the electrical properties of the electrolytes. Both types exhibited a monoclinic unit cell structure within the P21/m space group. Interestingly, the amorphous silica-based Li₄SiO₄ sample possessed a smaller particle size compared to the synthetic one. EDX analysis confirmed that the chemical compositions of both materials closely matched their intended formulations. The amorphous silica-based Li₄SiO₄ displayed 2.56 times higher total conductivity (4.61 × 10⁻⁵ S cm⁻¹) than that of synthetic silica-based Li₄SiO₄ at 500°C with bulk and grain boundary activation energy of 0.13 eV and 0.16 eV respectively at high temperature. Analysis of the conductivity–frequency spectra allowed estimation of the ionic hopping rate within the structures and found that the enhanced conductivity of the clay-based Li₄SiO₄ is attributed to higher mobile concentration compared to synthetic Li₄SiO₄.