Sintering, micro-structure and Li+ conductivity of Li7-xLa3Zr2-xNbxO12/MgO (x=0.2-0.7) Li-Garnet composite ceramics

Nb-doped Li7La3Zr2O12 (Nb-LLZO) is one of the promising electrolyte candidates in the Li-Garnet family due to its high Li-ion conductivity. The sintered Nb-LLZO ceramics, however, often exhibit abnormal grain growth with high porosity and poor mechanical properties. For advantaged electrochemical and mechanical properties, a uniform and dense microstructure is desired. In this research, MgO has been added as a secondary phase to inhibit abnormal grain growth in Nb-LLZO. The sintering process of the Nb-LLZO/MgO composite ceramics has been studied for different Nb doping levels (0.2-0.7 pfu) at sintering conditions of 1250 degrees C for 1-360 min. The ceramic density, microstructure, and Li-ion conductivity are reported. The composite ceramics have shown a very fast sintering speed. At 1250 degrees C, the 0.4Nb-LLZO/MgO composite can be well-sintered in 1 min. For sintering at 1250 degrees C for 40 min, ceramic samples showing relative density of 97%, conductivity of 6 x 10(-4) S cm(-1) at 25 degrees C, and activation energy of 0.40 eV are obtained.