Influence of sintering additives on densification and Li+ conductivity of Al doped Li7La3Zr2O12 lithium garnet

Garnet-like structured solid electrolyte Li7La3Zr2O12 (LLZ) in the cubic phase has received unique attention due to its high total (bulk + grain-boundary) Li+ conductivity combined with good chemical stability against lithium metal and commercial electrodes. In addition to the stabilization of high Li+ conductive cubic phase, the dense microstructure related to grains and grain-boundaries is also a critical issue for the successful application of LLZ as solid electrolyte membrane in all-solid-state lithium and lithium-air batteries. In this work, preparation of high Li+ conductive 0.9 wt% Al doped cubic LLZ i.e. Li6.16Al0.28La3Zr2O12 (Al-LLZ) by modified sol-gel technique and the influence of sintering additives on the density and total (bulk + grain-boundary) Li+ conductivity of the Al-LLZ are investigated. The present work reveals that among the three chosen sintering additives Li3BO3, Li3PO4 and Li4SiO4, Li4SiO4 appears to be a better sintering additive for the enhancement of the total (bulk + grain-boundary) Li+ conductivity and density of Al-LLZ. Among the investigated samples, Al-LLZ with 1 wt% of Li4SiO4 added and sintered at 1200 degrees C exhibits maximized total (bulk + grain-boundary) Li+ conductivity of 6.1 x 10(-4) S cm(-1) at room temperature (33 degrees C) along with the maximized density of 4.86 g cm(-3) (relative density of 96%).