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

Abstract

Perovskite-type compounds ABO 3 in which A = La, Li and B = Ti (Li 2/3 − 3x La x TiO 3 , 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 Ti 4 + can be easily reduced to Ti 3 + below this potential. Li 3/8 Sr 7/16 Ta 3/4 Zr 1/4 O 3 (LSTZ), in which A and B cations of SrZrO 3 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 Li 7 La 3 Zr 2 O 12 (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 SrTa 2 O 6 and Sr 2 Ta 2 O 7 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. • Perovskite Li–Sr–Ta–Zr–O solid electrolyte was prepared by powder-bed sintering. • Powder-bed sintering is effective to densify the pellet and reduce impurity phase. • Total ionic conductivity of Li–Sr–Ta–Zr–O pellet is above 2 × 10 − 4 S cm − 1 at 27 °C.