Synthesis and lithium-ion conductivity for perovskite-type Li3/8Sr7/16Ta3/4Zr1/4O3 solid electrolyte by powder-bed sintering

Perovskite-type compounds ABO3 in which A = La, Li and B = Ti (Li2/3 − 3xLaxTiO3, LLT) exhibit very high bulk ionic conductivity of 1.2 × 10− 3 S cm− 1 at 30 °C, but LLT has very large grain-boundary resistance and is only stable above 1.6–1.8 V vs. Li/Li+ because Ti4 + can be easily reduced to Ti3 + below this potential. Li3/8Sr7/16Ta3/4Zr1/4O3 (LSTZ), in which A and B cations of SrZrO3 are partially substituted by Li and Ta, has been reported to be more stable against the lithiated negative electrode than LLT. In this paper, we synthesized LSTZ by using “powder-bed sintering” method, which is commonly used for preparation of dense garnet-structured lithium-ion conductor Li7La3Zr2O12 (LLZ). At sintering process, the LSTZ pellet was covered with the same mother powder to suppress the excess Li loss during high temperature treatment and the formation of secondary phases. For LSTZ sintered with covering LSTZ mother powder, secondary phases such as SrTa2O6 and Sr2Ta2O7 were significantly reduced and LSTZ grains in the pellet were in good contact with each other. According to these improvement, the bulk and total (bulk + grain-boundary) ionic conductivity at 27 °C of LSTZ attained to 3.5 × 10− 4 S cm− 1 and 2.7 × 10− 4 S cm− 1, respectively. The total conductivity at room temperature is approximately 3 times higher than that as previously reported and comparable with LLT and LLZ.