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

Abstract

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. Li_6.16Al_0.28La₃Zr₂O₁₂ (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 °C exhibits maximized total (bulk + grain-boundary) Li⁺ conductivity of 6.1 × 10⁻⁴ S cm⁻¹ at room temperature (33 °C) along with the maximized density of 4.86 g cm⁻³ (relative density of 96%).