Innovative Design for the Enhancement of Lithium Lanthanum Titanate Electrolytes

Abstract

The high ionic conductivity in lithium lanthanum titanate perovskite ceramics, Li3x La(2/3)‑x TiO3 (LLTO), is well-known for the x ≈ 0.11 lithium concentration. The grain conductivity is approximately 10–3 S·cm–1 at room temperature, which makes this compound one of the best candidates for the development of solid-state electrolytes. However, lower grain boundary conductivity (10–6 to 10–4 S·cm–1) blocks lithium diffusion. In order to increase the total conductivity of LLTO ceramics, single crystal fibers of lanthanum aluminate (LAO) were inserted into its green ceramic matrix. Our hypothesis is that single crystal fibers are capable of inducting LLTO abnormal grain growth, thus improving the overall electrical conductivity of the composite. The results show that LAO single crystals act like seeds, creating abnormal grain growth at the LaAlO3 fiber surface. The impedance spectroscopy shows that the new composites have a substantial relative enhancement of total ionic conductivity (more than 200%) in comparison with the monolithic ceramic samples. This result shows the possibility of developing a novel composite design as a candidate for solid electrolyte applications.

Oriented Crystal Growth of La0.557Li0.330TiO3 in Bulk Ceramics Induced by LaAlO3 Single-Crystal Fibers

“…In a previous communication, we have shown the proof of this concept, 29 which creates the conditions for an increase in the conductance up to 200%, when compared to the conventional LLTO bulk ceramics. 29 However, some important aspects of the crystal growth process inside the bulk ceramics could not be explored at the time, especially regarding the possibility of crystallographic orientation and evolution of the crystal size with sintering temperature.…”

“…[100]-, [110]-, and [111]-oriented LAO crystal fibers with an average diameter of 0.5 mm were produced using the laser-heated pedestal growth (LHPG) technique. , The grown LAO crystal fibers were submitted to a surface cleaning process using organic solvents and ultrasound, before the composite synthesis. The typical LLTO powder with the chemical formula of LLTO was mixed by vibratory milling using yttria-stabilized zirconia balls with a diameter of 3 mm and isopropanol as the wet medium, and then the dried LLTO powder was sintered at 1100 °C for 12 h . The green body, a composite of the LLTO powder and LAO fiber, was prepared by hydraulic and isostatic pressing techniques, and the schematic diagram is shown in Figure .…”

“…In order to explore the influence of fiber orientation and sintering parameters on the LLTO crystal growth, three different sintering temperatures (1250, 1300, and 1350 °C) combined with four different sintering times (4, 6, 8, 10 h) were applied to treat the LLTO/[100]-LAO, LLTO/[110]-LAO, and LLTO/[111]-LAO composites. Detailed information about the experimental setup and powder synthesis can be found in our previous communication …”

“…Detailed information about the experimental setup and powder synthesis can be found in our previous communication. 29 X-ray Diffraction. In order to confirm the orientation of the obtained LLTO crystals, the MA-XRD patterns of the sintered composites were recorded using a Rigaku Ultima IV micro-area X-ray diffractometer in the angular range (2θ) from 20 to 90°with a scanning speed of 2°/min, accompanied with an irradiated area of 0.5 mm in diameter with a rotation speed of 60 RPM.…”

“…However, it has been difficult to grow LLTO single crystals from the melt due to their incongruent melting and the lithium loss during the crystal growth process. − Another approach is to control the abnormal grain growth inside the bulk ceramics, creating a LLTO crystal interconnecting the two electrodes. In a previous communication, we have shown the proof of this concept, which creates the conditions for an increase in the conductance up to 200%, when compared to the conventional LLTO bulk ceramics . However, some important aspects of the crystal growth process inside the bulk ceramics could not be explored at the time, especially regarding the possibility of crystallographic orientation and evolution of the crystal size with sintering temperature.…”