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

Li 0.33 La 0.56 TiO 3 (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 La 3+ (1.03 Å). In this study, to reduce lattice stress, we prepared Y-doped Li 0.33 La 0.56− x Y x TiO 3 ( x = 0.02, 0.05, 0.1) by using the sol-gel method. Because the ionic radius of Y 3+ is 0.90 Å, that is, larger than that of Li + (0.76 Å) and smaller than that of La 3+ (1.03 Å), Y 3+ suppresses the lattice distortion that prevents the formation of α -LLTO. The structural, morphological, and electrical characteristics of pure and Y 3+ -doped LLTO were investigated. The results show that Li 0.33 La 0.46 Y 0.1 TiO 3 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.