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Molten salt synthesis and characterization of fast ion conductor Li6.75La3Zr1.75Ta0.25O12

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Abstract

The limited electrochemical stability and the flammability of the liquid electrolytes presently used in Li-ion batteries stimulates the search for alternatives including ceramic solid electrolytes. Moreover, solid electrolytes also fulfil crucial functions in various large-scale energy storage systems, e.g. as anode-protecting membranes in aqueous Li-air batteries. Here, the processing of the solid electrolytes Li7La3Zr2O12 is studied for applications in Li-air batteries. Molten salt method (MSM) was adopted previously on synthesis of simple oxides; to the best of our knowledge, we report for the first time the adaptation of the MSM to prepare this class of solid electrolytes. As a model compound, we prepared the garnet-related Li6.75La3Zr1.75Ta0.25O12. It has been prepared by using stoichiometric amounts of La2O3, ZrCl4, and Ta2O5 in excess 0.88 M LiNO3:0.12 M LiCl molten salt. Subsequently, samples were heated to various temperatures in the range 600–900 °C for 6 h in air in a recrystallized alumina crucible and finally washed with distilled water to remove excess salts. The obtained Li6.75La3Zr1.75Ta0.25O12 electrolyte powder was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman, and impedance spectroscopy as well as surface area measurements. The cubic single phase was obtained for samples prepared at temperatures ≥700 °C. The effects of washing with water or aqueous LiOH solution on the structure and conductivity of the phases will be discussed.

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Acknowledgements

Authors wish to thank National Research Foundation, Prime Minister’s Office, Singapore for financial support under its Competitive Research Programme (CRP Award No. NRF-CRP 10-2012-6). Authors would like to thank Mr. Henche Kuan, Dept. of MSE, NUS for recording XPS data.

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  1. Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore

    M. V. Reddy & S. Adams

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  1. M. V. Reddy
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  2. S. Adams
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Correspondence to S. Adams.

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Contribution to Symposium A: “Advances in Energy Storage Systems: Lithium Batteries, Supercapacitors and Beyond”, during ICMAT 2015, June 28–July 3, Singapore

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Reddy, M.V., Adams, S. Molten salt synthesis and characterization of fast ion conductor Li6.75La3Zr1.75Ta0.25O12 . J Solid State Electrochem 21, 2921–2928 (2017). https://doi.org/10.1007/s10008-017-3615-2

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