Preparation of (La, Li)TiO 3 Dense Ceramics using Sol-Gel and Ion-Exchange Process
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Preparation of (La, Li)TiO3 Dense Ceramics using Sol-Gel and Ion-Exchange Process Seiichi Suda, Hiroyuki Ishii and Kiyoshi Kanamura Graduate School of Engineering, Tokyo Metropolitan University, 1-1 Minami-Ohsawa, Hachioji, Tokyo 192-0397, Japan.
ABSTRACT Lithium ionic conductor, (La, Li)TiO3, has synthesized with La/Li-TiO2 amorphous spheres that were obtained by sol-gel and ion-exchange method, and succeeding La3+/Li+ partial ion exchange. In this work, La3+/Li+ ion exchange conditions were mainly investigated in order to obtain dense (La, Li)TiO3 ceramics that have highly ionic conductivities. La3+/Li+ ion exchange behavior was changed with ion-exchange solutions, and the Li/Ti ratio was increased with an increase in ethanol/water ratio in the solvent used for La3+/Li+ partial ion exchange. The use of an adequate ethanol/water ratio resulted in La/Li-TiO2 amorphous spheres with the composition of La/Li/Ti=0.54/0.34/1.00, and sintering of the spheres at 1200oC for 5 h in air led to dense (La, Li)TiO3 ceramics which exhibit the conductivity of 4.0 10-3 S cm-1 at 25 .
INTRODUCTION Perovskite-type lanthanum lithium titanate, (La, Li)TiO3, has highly lithium ionic conductivity, which exhibits more than 10-3 S cm-1 at room temperature [1-3]. This ceramic can be applicable to solid electrolyte of all-solid-state rechargeable lithium batteries or gas sensing devices such as NOx and SOx because of high ionic conduction. The conductivity of (La, Li)TiO3 depends on A-site occupancy of lithium ions, lanthanum and vacancy, which is formed by introducing lanthanum ions into the sites, because lithium ions pass through A-sites of the perovskite structure. Therefore, precise control of the compositions is indispensable to obtain (La, Li)TiO3 ceramics that exhibit high lithium ionic conductivity at room temperatures. Both experimental results for (La, Li)TiO3 ceramics synthesized by solid-state reactions and simulation results applied by three-dimensional percolation theory have revealed the relationship between the compositions and lithium ionic conductivity for (La, Li)TiO3 and the highest bulk conductivity, which was reported to be 1.5x10-3 S cm-1 at 23oC, was provided at the lithium composition of 3x=0.34 in the expression of La2/3-xLi3x 1/3-2xTiO3 vacancy [4-6]. Application of lithium ion conductors, such as (La, Li)TiO3 ceramics, to solid electrolytes of rechargeable lithium ionic batteries requires high lithium ionic conductivity not only in bulk but also at grain boundaries. The sintering of (La, Li)TiO3 ceramics generally requires to be at temperatures higher than 1350oC, and the conductivities at grain boundaries exhibit extremely lower than that in bulk. We have synthesized (La, Li)TiO3 ceramics using amorphous spheres in order to increase density of the ceramics and conductivity derived from grain boundaries. (La, Li)TiO3 ceramics was thus obtained by La/Li-TiO2 amorphous spheres (LLT particles). LLT particles were synthesized by partial ion-exchange between lanthanum ions and lithium in Li-TiO2 amorp
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