Effect of Nano-sized Al₂O₃ Addition on the Sintering Density of Garnet-type Solid Electrolytes

Abstract

Garnet-like oxide lithium ionic conductor Li₇La₃Zr₂O₁₂ (LLZO) exhibits relatively high ionic conductivity and electrochemical stability against lithium metals, attracting much attention as a solid electrolyte for all-solid-state lithium metal batteries. However, for practical use, the improvement in the ionic conductivity of the grain boundaries and sinterability of LLZO is necessary. Nano-sized fumed Al₂O₃ prepared by the vapor phase with various specific surface areas as a sintering aid has been applied to the garnet-type lithium ionic conductor, Li_6.25Ga_0.25La₃Zr₂O₁₂ (LGLZ) and Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZT). The addition effect of fumed Al₂O₃ on lattice parameters, particle morphology, sinterability, and ionic conductivity has been investigated. The sinterability has improved by the addition of nano-sized fumed Al₂O₃ with a high specific surface area, and ionic conductivity does not exhibit a significant change for LGLZ. The addition of fumed Al₂O₃ with a specific surface of 130 m² g⁻¹ has lowered the sintering temperature of LLZT by 200 °C, which indicates nano-sized Al₂O₃ is quite useful as a sintering aid for garnet-type solid electrolytes.