Structural and Electrical Effects of Y-doped Li_0.33La_0.56−xY_xTiO₃ Solid Electrolytes on All-Solid-State Lithium Ion Batteries

Abstract

Li_0.33La_0.56TiO₃ (LLTO) solid state electrolytes have been considered as candidates to substitute for organic liquid electrolytes in lithium batteries. LLTO consist of a mixture of cubic phases with Pm3m symmetry (α-LLTO) and with tetragonal P4/mmm symmetry (β-LLTO). The α-LLTO phase has a higher Li ion conductivity than the β-LLTO phase. However, α-LLTO is characterized by high lattice strain, which induces the formation of β-LLTO due to the different atomic sizes of Li⁺ (0.76 Å) and La³⁺ (1.03 Å). In this study, to reduce lattice stress, we prepared Y-doped Li_0.33La_0.56−xY_xTiO₃ (x = 0.02, 0.05, 0.1) by using the sol-gel method. Because the ionic radius of Y³⁺ is 0.90 Å, that is, larger than that of Li⁺ (0.76 Å) and smaller than that of La³⁺ (1.03 Å), Y³⁺ suppresses the lattice distortion that prevents the formation of α-LLTO. The structural, morphological, and electrical characteristics of pure and Y³⁺-doped LLTO were investigated. The results show that Li_0.33La_0.46Y_0.1TiO₃ exhibits a better bulk conductivity (σ = 9.51 × 10⁻⁴ S cm⁻¹) at 25 °C due to the increasing volume fraction of the more conductive α-LLTO phase.