Conditions Extrêmes et Matériaux : Haute Température et Irradiation
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2022

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Ö.U.Kudu, T.Famprikis, S.Cretu, B.Porcheron, E.Salager, A.Demortiere, M.Courty, V.Viallet, T.L.Mercier, B.Fleutot, M.-D.Braida, C.Masquelier, 'Structural details in Li3PS4: variety in thiophosphate building blocks and correlation to ion transport', Energy Storage Mater. 44 168-179 (2022) doi:10.1016/j.ensm.2021.10.021

Li3PS4 is an attractive solid-electrolyte material that possesses high RT ionic conductivity (10-4 S.cm−1) but the effects of specific synthesis parameters on the material's local structure and transport properties still demand clarifications. Herein, we highlight the substantial effects of cooling breaks in the mechanochemical synthesis procedure on the formation of a variety of PxSya− moieties and on the transport properties of Li3PS4, through Raman and impedance spectroscopy measurements. We show that ball-milled Li3PS4 (with no subsequent annealing), which is often regarded as “amorphous/glass/glassy Li3PS4”, is not fully amorphous using X-ray diffraction and transmission electron microscopy. Upon subsequent annealing for 1 hour above 190°C, β-Li3PS4 is crystallized and our 31P magic angle spinning nuclear magnetic resonance spectra suggest that 3 distinct PS43− moieties form, which we refer to as amorphous-, β- and ϒ-type units. Herein, we present a hypothesis to explain the correlation between the ionic conductivity and the distinct PS43− units as a function of the annealing temperature. Our results consolidate the recent reports noting that crystallization of β-Li3PS4 is not necessary to obtain a high conductivity in ball-milled Li3PS4. Finally, we introduce a phase mixture between β-Li3PS4 and ϒ-Li3PS4 synthesized at 200°C, which is the lowest synthesis temperature yet for ϒ-Li3PS4.