Sr- and Nb-co-doped Li7La3Zr2O12 solid electrolyte with Al2O3 addition towards high ionic conductivity

Abstract

In the present study, series of garnet-type Li6.75+xLa3−xSr x Zr1.75Nb0.25O12 solid electrolytes [LLSZN with various Sr contents (x = 0.05–0.25)] have been prepared via conventional solid-state method. The effects of Sr contents on their phase structure and ionic conductivity have been systematically investigated on the combined measurements of X-ray diffraction and scanning electron microscopy and alter current impedance spectroscopy. Our results reveal that a phase transition from tetragonal to cubic structure occurs when both Sr and Nb elements is introduced, and such a cubic structure can be stable over the whole Sr contents variation, which is suggested to provide a beneficial impact on the performance of LLSZN. Accordingly, both relative density and total ionic conductivity exhibit a favorable tendency of increasing first and then decreasing with increased Sr contents, wherein a peak value at 93.46% and 5.09 × 10−4 S cm−1, respectively, can be well achieved. Particularly, the maximum ionic conductivity is almost twice that of the compared sample (2.93 × 10−4 S cm−1), and possess the minimum activation energy ~ 0.30 eV. Such a modification method, featured with higher efficiency and lower cost, is expected to be helpful for the development of solid electrolyte.