Structural and Electrical Effects of Y-doped Li0.33La0.56−xYxTiO3 Solid Electrolytes on All-Solid-State Lithium Ion Batteries

Abstract

Li0.33La0.56TiO3 (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 A) and La3+ (1.03 A). In this study, to reduce lattice stress, we prepared Y-doped Li0.33La0.56−xYxTiO3 (x = 0.02, 0.05, 0.1) by using the sol-gel method. Because the ionic radius of Y3+ is 0.90 A, that is, larger than that of Li+ (0.76 A) and smaller than that of La3+ (1.03 A), 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 Li0.33La0.46Y0.1TiO3 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.