An innovative synthesis: Garnet lithium-ion conductive solid-state electrolyte synthesized by an arc melting process
PRADEILLES S. 2,3, NONNET E. 3, GABAUDAN V. 3, SIMON P. 2, TABERNA P. 2, ROZIER P. 2
1 CIRIMAT / Saint-Gobain, Toulouse, France; 2 CIRIMAT, Toulouse, France; 3 Saint-Gobain Research Provence, Cavaillon, France
All-solid-state batteries (ASSB) have drawn a real scientific interest in the last decade, guided by new electrolyte ceramic materials discovery. Among them, Li6,6La3Zr1,6Ta0,4O12, a garnet?type electrolyte (LLZO:Ta) shows close to equal ionic conductivity compared to conventional liquid ones . Its high mechanical properties guaranty use of lithium metal at the anode, allowing an important gain in terms of energy density [2, 3]. However, though (electro?)chemical stable vs. lithium metal, LLZO:Ta suffers from air sensitivity  and requires many synthesis steps with parameters drastically affecting the properties of the as obtained material  as well as the shaping procedure.
In this report we propose a new, efficient, fast and one?step synthesis of LLZO:Ta by direct moulding of the fused raw materials, using arc melting process. We will show that this process allows getting in one?step dense cubic LLZO:Ta (relative density above 95%) with ionic conductivity determined using Electrochemical Impedance Spectroscopy close to bulk properties of LLZO:Ta showing the perfect mastering of grain boundaries. These properties are maintained even for samples stored in ambient air using a simple anhydrous polishing of the part indicating that only the surface is protonated thanks to high density.
Moreover, we will present operando XRD characterization of LLZO:Ta/ NMC 811 powder mixture which shows high thermal and chemical stability of the catholyte mixture in a wide range of temperature. We will also show that the powder was used to successfully prepare, using Spark Plasma Sintering technique, both electrolyte separator membranes with relative density above 98% and positive electrode composites NMC 811/LLZO:Ta (70/30 vol%).
This report will allow concluding that the as prepared LLZO:Ta is perfectly adapted to be used as ionic conductor in the different components of Li-ASSB while the remaining issue lies in the limited thermal chemical stability of the active material itself.
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