Effect of Nano-sized Al2O3 Addition on the Sintering Density of Garnet-type Solid Electrolytes (Supporting Information)

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, Li6.25Ga0.25La3Zr2O12 (LGLZ) and Li6.5La3Zr1.5Ta0.5O12 (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.