Synthesis and Characterization of Impurity-Free Li6/16Sr7/16Ta3/4Hf1/4O3 Perovskite as a Solid-State Lithium-Ion Conductor

Perovskite-type lithium-ion conductors are a potential class of solid-state electrolytes for solid-state batteries due to their excellent environmental stability, good mechanical strength, reasonably wide electrochemical stability window, and high ionic conductivity. A-site deficient Li6/16Sr7/16Ta3/4Hf1/4O3 is a promising perovskite composition identified, but it is prone to form impurity phases during synthesis, which introduces high grain bounary resistance to the total ionic conductivity. A systematic investigation is reported on the effect of the synthesis conditions (e.g., excess Li, sintering temperature, and mother powder protection) on the phase composition and properties of this perovskite. The results show that the mother powder bed protection and 1450 °C sintering temperature without Li compensation are the best conditions to achieve single phase. The single-phase sample exhibits 96% theoretical density, a bulk ionic conductivity of 0.408 mS cm−1, and an electronic conductivity of 3.6 × 10−9 S cm−1 at 25 °C with an activation energy of 0.352 eV, Young s modulus of 63.91 GPa, and shear modulus of 26.16 GPa. However, Li6/16Sr7/16Ta3/4Hf1/4O3 is unstable against lithium metal and can be reduced readily. Alternative anode materials or surface protection layers are needed if it is considered as an electrolyte for lithium-metal based solid-state lithium-ion batteries.