Ionic Conductivity and Microstructure of Li₄GeO₄-Based Solid Electrolytes

Abstract

Li₄GeO₄-based solid electrolytes can be synthesized at low temperatures, and their formability is improved by adding Li₂SO₄. Glass–ceramic Li₄GeO₄ exhibits a relatively high ionic conductivity of approximately 10⁻⁶ S cm⁻¹ at room temperature, which is higher than that of glass Li₄GeO₄. Thus, Li₄GeO₄ has promising applications in all-solid-state lithium ion batteries. To understand the correlation between the ionic conductivity, formability, and microstructure of the synthesized materials, the microstructures and crystallization process of glass and glass–ceramic Li₄GeO₄ and 80Li₄GeO₄·20Li₂SO₄ (Li_3.6Ge_0.8S_0.2O₄) were observed by transmission electron microscopy (TEM). Since Li_3.6Ge_0.8S_0.2O₄ glass exhibits a halo diffraction pattern, the addition of Li₂SO₄ to Li₄GeO₄ stabilizes its amorphous phase. In addition, glass–ceramic samples were found to be characterized by an amorphous state containing nanocrystallites with a crystallinity degree of approximately 40%, which improves the ionic conductivity of the material.