Effect of Sr and Nb co-doped on the total conductivity of Li0.5La0.5TiO3 ceramic electrolytes

Abstract

The solid electrolyte Li0.5La0.5TiO3 is widely used in solid-state batteries due to its high grain conductivity at room temperature (RT). However, the ever-increasing requirement for high ionic conductivity necessitates the improvement of its total conductivity. In this study, tuning the total conductivity of perovskite-type La2/3-xLi3xTiO3 (LLTO) membranes through a co-doping strategy was proposed and systematically investigated, Here, an Li0.5−y+x Sr x La0.5−x Ti1−y Nb y O3 (LLSTN, x = 0, 0.04, 0.06, 0.08, and 0.1 mol%) ceramic solid electrolyte was prepared via the conventional solid-state reaction method. The introduction of Sr2+ and Nb5+ increases the lithium-ion vacancies and transforms the Li0.5La0.5TiO3 crystal structure from tetragonal to cubic. On the other hand, the lattice constant becomes larger, causing the migration channel of the lithium ions to become larger. Meanwhile, with the increase of Nb5+ doping amount, lithium lanthanum niobate forms between grains, inhibiting grain growth and it helps to reduce the resistance of lithium ion migration at grain boundaries. The total conductivity of sample Li0.5La0.42Sr0.08Ti0.92Nb0.08O3 reaches 5.10 × 10−5S·cm−1 at RT, which is about six times higher than that of the undoped sample, and the activation energy is 0.28 eV.