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American Chemical Society, Chemistry of Materials, 6(28), p. 1861-1871, 2016

DOI: 10.1021/acs.chemmater.6b00038

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Crystal structure of garnet-related Li-ion conductor Li 7−3 x Ga x La 3 Zr 2 O 12 : Fast Li-ion conduction caused by a different cubic modification?

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Li-oxide garnets such as Li7La3Zr2O12 (LLZO) are among the most promising candidates for solid-state electrolytes to be used in next generation Li-ion batteries. The garnet-structured cubic modification of LLZO, showing space group Ia-3d, has to be stabilized with supervalent cations. LLZO stabilized with Ga3+ shows superior properties compared to LLZO stabilized with similar cations; however, the reason for this behavior is still unknown. In this study, a compre-hensive structural characterization of Ga-stabilized LLZO is performed by means of single crystal X-ray diffraction. Coarse-grained samples with crystal sizes of several hundred µm are obtained by solid state reaction. Single crystal X-ray diffraction results show that Li7−3xGaxLa3Zr2O12 with x > 0.07 crystallizes in the acentric cubic space group I-43d. This is the first definite record of this cubic modification for LLZO materials and might explain the superior electrochemical performance of Ga-stabilized LLZO compared to its Al-stabilized counterpart. The phase transition seems to be caused by the site preference of Ga3+. 7Li NMR spectroscopy indicates an additional Li-ion diffusion process for LLZO with space group I-43d compared to space group Ia-3d. Despite all efforts undertaken to reveal structure-property relationships for this class of materials, this study highlights the potential for new discoveries.