Symmetry Effect on the Enhancement of Lithium-Ion Mobility in Layered Oxides Li2A2B2TiO10 (A = La, Sr, Ca; B = Ti, Ta)

• Published in: Journal of physical chemistry. C 2021-02, Vol.125 (7), p.3689-3697
• Main Authors: Fanah, Selorm Joy, Ramezanipour, Farshid
• Format: Article
• Language: English
• Subjects: C: Energy Conversion and Storage
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.0c09294

The effect of the symmetry variation on lithium-ion mobility has been examined through synthesis, neutron and X-ray diffraction, electrochemical impedance, dielectric, and modulus studies of five layered compounds, Li2La2Ti3O10, Li2SrLaTaTi2O10, Li2Sr2Ta2TiO10, Li2CaLaTaTi2O10, and Li2Ca2Ta2TiO10. All five materials, Li2A2B2TiO10, feature stacks comprising three layers of BO6 octahedra, similar to the so-called Ruddlesden–Popper (RP) structure. The stacks are separated by lithium ions. While Li2La2Ti3O10 has a typical RP structure, the other four compounds feature lower symmetry, as confirmed by Rietveld refinements using X-ray and neutron diffraction data. The latter structure has a supercell, ∼√2a × ∼√2b × ∼1c, resulting in the distribution of lithium ions over two distinct sites. The change in symmetry has a positive effect on ionic mobility. However, this effect can be opposed or reinforced by the impact of Li–Li distances, grain size, and grain contact. In the most conductive material, Li2Ca2Ta2TiO10, the effect of structural change is reinforced by good grain contact and shorter Li–Li distances due to the incorporation of the smaller Ca2+ ions, which facilitate the hopping of lithium ions between different sites. The effect of these parameters is revealed through detailed analyses of real and imaginary components of electrochemical impedance, modulus, and dielectric properties, which demonstrate the enhanced mobility of lithium ions.