Densification of Ta-Doped Garnet-Type Li6.75La3Zr1.75Ta0.25O12 Solid Electrolyte Materials by Sintering in a Lithium-Rich Air Atmosphere

Garnet-type Li7La3Zr2O12 (LLZO) has attracted much attention because it shows promising properties for all-solid-state lithium-ion batteries. A dense microstructure is needed to obtain a high Li+ conductivity, as porous microstructures result in much lower Li+ conductivities. In this work, tantalum-doped cubic garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZTO) with a relative density of 92% was prepared by a simple co-precipitation method with cold uniaxial pressing and sintering in a lithium-rich air atmosphere, which was created by the addition of LiOH to the LLZTO cover powder. This LiOH-containing cover powder (15Li + LiOH) has been shown to improve densification and increase the room temperature total conductivity to 6.9 × 10−4 S/cm with an activation energy of 0.2 eV. This 15Li + LiOH cover powder results in the formation of an Al-containing interparticle phase, which facilitates the densification of LLZTO. The aluminum concentration increases during sintering and is located in the grain boundary.