Microstructural and Electrochemical Properties of Alkaline Earth Metal-Doped Li Garnet-Type Solid Electrolytes Prepared by Solid-State Sintering and Spark Plasma Sintering Methods

Li-stuffed garnet-type solid Li-ion electrolytes have been considered as a promising candidate for all-solid-state Li batteries. In this work, alkaline earth metal-doped Li garnet-type solid Li-ion electrolytes, Li6.5La2.5A0.5TaZrO12 (A = Ca, Sr, Ba) were prepared by conventional solid-state sintering (CSS) and spark plasma sintering (SPS) methods. The effect of sintering methods on the structural and electrochemical properties of the solid electrolytes was investigated by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). Among the investigated compounds, Sr-doped garnet-type Li6.5La2.5Sr0.5TaZrO12 prepared by the SPS method showed the highest Li-ion conductivity of 3.08 × 10–4 S cm–1 at 20 °C and the lowest activation energy of 0.35 eV. Both Sr- and Ba-doped samples exhibited a critical current density of 0.15 mA cm–2, and the Sr-doped Li6.5La2.5Sr0.5TaZrO12 sample showed the lowest Li-ion charge-transfer resistance of 139 Ω cm2 at room temperature.