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Experimental Assessment of the Practical Oxidative Stability of Lithium Thiophosphate Solid Electrolytes

preprint
revised on 09.09.2019 and posted on 09.09.2019 by Georg Dewald, Saneyuki Ohno, Marvin Kraft, Raimund Koerver, Paul Till, Nella Vargas, Juergen Janek, Wolfgang Zeier

All-solid-state batteries are often expected to replace conventional lithium-ion batteries in the future. However, the practical electrochemical and cycling stability of the best-conducting solid electrolytes, i.e. lithium thiophosphates, are still critical issues that prevent long-term stable high-energy cells. In this study, we use stepwisecyclic voltammetry to obtain information on the practical oxidative stability limit of Li10GeP2S12, a Li2S‑P2S5glass, as well as the argyrodite Li6PS5Cl solid electrolytes. We employ indium metal and carbon black as the counter and working electrode, respectively, the latter to increase the interfacial contact area to the electrolyte as compared to the commonly used planar steel electrodes. Using a stepwise increase in the reversal potentials, the onset potential at 25 °C of oxidative decomposition at the electrode-electrolyte interface is identified. X‑ray photoelectron spectroscopy is used to investigate the oxidation of sulfur(-II) in the thiophosphate polyanions to sulfur(0) as the dominant redox process in all electrolytes tested. Our results suggest that after the formation of these decomposition products, significant redox behavior is observed. This explains previously reported redox activity of thiophosphate solid electrolytes, which contributes to the overall cell performance in solid-state batteries. The stepwise cyclic voltammetryapproach presented here shows that the practical oxidative stability at 25 °C of thiophosphate solid electrolytes against carbon is kinetically higher than predicted by thermodynamic calculations. The method serves as an efficient guideline for the determination of practical, kinetic stability limits of solid electrolytes.

Funding

Bundesministerium für Bildung und Forschung (BMBF) 03XP0115A

History

Email Address of Submitting Author

wolfgang.g.zeier@pc.jlug.de

Institution

Justus-Liebig-University Giessen

Country

Germany

ORCID For Submitting Author

0000-0001-7749-5089

Declaration of Conflict of Interest

no conflict of interest

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