A review on structural characteristics, lithium ion diffusion behavior and temperature dependence of conductivity in perovskite-type solid electrolyte Li3xLa2∕3−xTiO3

Abstract

Due to various and indefinite Li-ion distributions within the cuboctahedron surrounded by eight TiO6 and local subtle distortions, perovskite-type solid electrolyte Li[Formula: see text]La[Formula: see text]TiO3 (LLTO) is suitable to be used as a model system for studying the structure–conductivity relationship. This review is focused on structural characteristics, Li-ion diffusion behavior and conductivity in LLTO. Li-ion concentration, cooling rate of heat treatment and heating temperature are shown to be three main factors influencing the space group structure of LLTO, involving the distributions of Li, La ions and vacancies as well as the distortion of TiO6 octahedron. In rhombohedral and some orthorhombic phases, Li ions partially occupy O4 windows of cuboctahedrons, whose diffusion could be described by the bond percolation model, whereas in other phases with Li ions inside the cuboctahedrons, the site percolation model is applicable to Li-ion conduction. Li-ion conductivity versus temperature curve exhibits non-Arrhenius behavior, which is divided into three sections with different activation energies, although its first-derivative is continuous. The activation energy is correlated closely with the tilting angle of TiO6 octahedron, both of which decrease with the increase of temperature. Experimental studies and theoretical results are discussed in parallel to provide insight into the detailed structure-conductivity relationship.