Investigation on the stability of Li 5 La 3 Ta 2 O 12 lithium ionic conductors in humid environment

Abstract

In this paper, the stability in humid air of Li₅La₃Ta₂O₁₂ lithium ionic conductors synthesized by conventional solid-state reaction was investigated by internal friction, conductivity, weight variation, X-ray diffraction, and thermogravimetric analysis methods. It was found that when the Li₅La₃Ta₂O₁₂ samples were aged in open air at room temperature, the internal friction peaks associated with the short-distance diffusion of lithium vacancies gradually shift toward higher temperature and increase in height, while the weight of the sample increases and impurity phases of LiOH·H₂O appear. These results reveal that the Li₅La₃Ta₂O₁₂ compounds are unstable against moisture in open air at room temperature. It was suggested that the protons from the moisture substitute the lithium ions in Li₅La₃Ta₂O₁₂ samples to form Li₂O and new protonic derivatives, Li_5−xLa₃Ta₂O_12−x(OH)_x (0<x<2.15), and the resultant Li₂O may react further with water to form LiOH·H₂O.

Keywords

lithium ionic conductor / Li5La3Ta2O12 / internal friction (IF)