Role of Pairwise Reactions on the Synthesis of Li_0.3La_0.57TiO₃ and the Resulting Structure–Property Correlations

Abstract

The performance of single-ion conductors is highly sensitive to the material’s defect chemistry. Tuning these defects is limited for solid-state reactions as they occur at particle–particle interfaces, which provide a complex evolving energy landscape for atomic rearrangement and product formation. In this report, we investigate the (1) order of addition and (2) lithium precursor decomposition temperature and their effect on the synthesis and grain boundary conductivity of the perovskite lithium lanthanum titanium oxide (LLTO). We use an intimately mixed sol–gel, a solid-state reaction of Li precursor + La2O3 + TiO2, and Li precursor + amorphous La0.57TiO x as different chemical routes to change the way in which the elements are brought together. The results show that the perovskite can accommodate a wide range of Li deficiencies (upward of 50%) while maintaining the tetragonal LLTO structure, indicating that X-ray diffraction (XRD) is insufficient to fully characterize the chemical nature of the product (i.e., Li-deficient LLTO may behave differently than stoichiometric LLTO). Variations in the relative intensities of different reflections in XRD suggest variations in the La ordering within the crystal structure between synthesis methods. Furthermore, the choice of the precursor and the order of addition of the reactants lower the time required to form a pure phase. Density functional theory calculations of the formation energy of possible reaction intermediates support the hypothesis that a greater thermodynamic driving force to form LLTO leads to a greater LLTO yield. The retention of lithium is correlated with the thermal decomposition temperature of the Li precursor and the starting material mixing strategy. Taking the results together suggests that cations that share a site with Li should be mixed early to avoid ordering. Such cation ordering inhibits Li motion, leading to higher Li ion resistance.

Memory Effect on the Synthesis of Perovskite-Type Li-Ion Conductor LixLa2/3–x/3TiO3 (LLTO)

“…21 The observation that a high synthesis temperature is necessary is also in agreement with previously reported syntheses, which all utilized temperatures > 1200 °C. 21,22,24,25,27,29,30,32,33,61 The different precursors have led to the formation of polymorphs. This result is unusual as at the synthesis temperature of 1300 °C, LLTO should be present in the cubic Pm-3m polymorph, 21 yet as the sample cools with the same cooling conditions (5 °C min −1 ), different polymorphs are stabilized.…”

“…21 The double-perovskite P4/mmm structure has also been reported at room temperature. 30,32 The P4/nbm structure transforms into the double perovskite (before ultimately transforming to Pm-3m), whereas the I4/mcm structure transitions into the PC structure. These results indicate that the synthesis conditions are highly important to the structure.…”

“…Recently, Malkowski et al reported that varying the precursors and synthesis methods affects the La1 (green spheres in Figure ) and La2 (dark green spheres in Figure ) site occupancies in P 4/ mmm LLTO. They also performed a sol–gel synthesis to make a La 0.57 TiO x precursor, which then reacted with LiNO 3 at 700 °C to form Li 0.3 La 0.57 TiO 3 instead of the much higher temperatures of 1200 °C. , This enabled better stoichiometry control by avoiding lithium loss.…”

Practical Application of All‐Solid‐State Lithium Batteries Based on High‐Voltage Cathodes: Challenges and Progress

“…The oxide electrolytes can generally divided into garnet-type Li 7 La 3 Zr 2 O 12 (LLZO), NASICON-type LiTi 2 (PO 4 ) 3 , LiSICONtype Li 14 Zn(GeO 4 ) 4 , and Perovskite-type La 0.5 Li 0.5 -dTiO 3 (LLTO). [15,[97][98][99] Due to the large rigidity of the oxide electrolyte, many methods have been employed to fabricate relatively dense and well-contacted oxide mixtures. Qin et al introduced nano La 2 O 3 as an effective additive to promote the uniform distribution of Li 6.5 La 3 Zr1.5Ta 0.5 O 12 particles, as well as to construct a 3D lithium-ion transport network along the grain boundary.…”

A Comparative View of Alkaline and Alkaline-Earth Element Intercalation into Perovskite-Type AxLayTiO3 (A = Li, Na, or Mg) Based on Theoretical Calculations and Experiments

“…Perovskite-type lithium lanthanum titanate Li 0.5 La 0.5 TiO 3 (LLTO) and structurally related sodium lanthanum titanate Na 0.5 La 0.5 TiO 3 (NLTO) are being studied as potential solid electrolytes for solid-state batteries, which would be advantageous in terms of safety compared to batteries based on liquid electrolytes. − It was found that LLTO is much more promising than NLTO for its similar structure with space group P 4/ mmm . Lanthanum ions are a main contribution for the stabilization of the crystalline structure, while lithium ions are the charge carriers, and the La layers can block the diffusion of the mobile ions.…”