Synthesis, Crystal Structure, and Stability of Cubic Li7-xLa3Zr2-xBixO12.

Reinhard Wagner,Emmanuelle Suard,Maurizio E. Musso,Georg Amthauer,Günther J. Redhammer,Daniel Rettenwander,Bernhard Stanje,Martin Wilkening,Gerold Tippelt,Gebhard Sabathi

doi:10.1021/acs.inorgchem.6b01825

Reinhard Wagner, Emmanuelle Suard + Show 8 more

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https://doi.org/10.1021/acs.inorgchem.6b01825

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Abstract

Li oxide garnets are among the most promising candidates for solid-state electrolytes in novel Li ion and Li metal based battery concepts. Cubic Li7La3Zr2O12 stabilized by a partial substitution of Zr4+ by Bi5+ has not been the focus of research yet, despite the fact that Bi5+ would be a cost-effective alternative to other stabilizing cations such as Nb5+ and Ta5+. In this study, Li7–xLa3Zr2–xBixO12 (x = 0.10, 0.20, ..., 1.00) was prepared by a low-temperature solid-state synthesis route. The samples have been characterized by a rich portfolio of techniques, including scanning electron microscopy, X-ray powder diffraction, neutron powder diffraction, Raman spectroscopy, and 7Li NMR spectroscopy. Pure-phase cubic garnet samples were obtained for x ≥ 0.20. The introduction of Bi5+ leads to an increase in the unit-cell parameters. Samples are sensitive to air, which causes the formation of LiOH and Li2CO3 and the protonation of the garnet phase, leading to a further increase in the unit-cell parameters. The incorporation of Bi5+ on the octahedral 16a site was confirmed by Raman spectroscopy. 7Li NMR spectroscopy shows that fast Li ion dynamics are only observed for samples with high Bi5+ contents.

Highlights

Li stuffed oxide garnets have received much scientific attention as fast Li ion conductors
Results from 7Li nuclear magnetic resonance (NMR) spectroscopy show that fast Li ion diffusivity for LLZBO is only achieved for high Bi contents
The results of Xia et al show that an increase of the density of samples, either by higher sintering temperatures or by the introduction of Al3+ that acts as a sintering aid, are beneficial for the Li ion conductivity

Summary

Introduction

Li stuffed oxide garnets have received much scientific attention as fast Li ion conductors. The cubic polymorph can be stabilized at room temperature by doping with supervalent cations such as Al3+,2,5−8 Fe3+,9,10 and Ga3+,11−14 which are incorporated on the 4-fold coordinated 24d/96h positions replacing Li+, Ce4+ replacing La3+ on the 8-fold coordinated 24c position,[15] and Mo6+,16,17 Nb5+,18 Ta5+,12,13,19−21 Sb5+,22 Te6+,23 W6+,24 and Y3+25 replacing Zr4+ at the octahedrally coordinated 16a position. It was recently shown by Xia et al that a stabilization of the cubic Ia3̅d modification can be achieved by a partial substitution of Zr4+ with Bi5+; the end member Li5La3Bi2O12 (LLBO) was already described by Murugan et al and further discussed in several other studies.[26−30].

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