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Lithium ion conducting argyrodites are among the most studied solid electrolytes due to their high ionic conductivities. A major concern in a solid-state battery is the solid electrolyte stability. Here we present a systematic study on the influence of cationic and anionic substitution on the electrochemical stability of Li6PS5X, using step-wise cyclic voltammetry, optical band gap measurements, hard X-ray photoelectron spectroscopy along with first-principles calculations. We observe that going from Li6PS5Cl to Li6+xP1-xMxS5I (M = Si4+, Ge4+), the oxidative degradation does not change. Considering the chemical bonding shows that the valence band edges are mostly populated by non-bonding orbitals of the PS43- units or unbound sulfide anions and that simple substitutions in these sulfide-based solid electrolytes cannot improve oxidative stabilities. This work provides insights on the role of chemical bonding on the stability of superionic conductors and shows that alternative strategies are needed for long-term stable solid-state batteries.

Superionic lithium argyrodites are attractive as solid electrolytes for all-solid-state-batteries. These materials of composition Li6PS5X (X = Cl, Br, and I) exhibit structural disorder between the X−/S2− positions, with higher disorder realizing better Li+ transport. Further replacement of the sulfide by chloride anions (for the series Li7−xPS6−xClx) has been shown to increase the ionic conductivity. However, the underlying changes to the lithium substructure are still relatively unknown. Here we explore a larger range of nominal halide compositions in this material from x = 0.25 to x = 1.5 and explore the changes with neutron diffraction and impedance spectroscopy. The replacement of S2− by Cl−causes a lowered average charge in the center of the prevalent Li+ “cages”, which in turn causes weaker interactions with Li+ ions. Analysis of neutron diffraction data reveals that the increased Cl− content causes these clustered Li+ “cages” to become more interconnected, thereby increasing Li+ conductivity through the structure. This study explores the understanding of the fundamental structure–transport correlations in the argyrodites, specifically structural changes withinthe Li+ ion substructure upon changing anionic charge distribution.

The quantitative influence of microstructure, porosity, surface area, and changes in the crystal lattice on the electric conduction mechanisms in cathode-active materials for lithium ion batteries ...

Driven by the rising demand for consumer electronics, the field of all solid-state batteries employing solid electrolytes as the ion-conducting separator has attracted enormous attention in the las...

Driven by the increasing attention that the superionic conductors Li3MX6 (M = Y, Er, In, La; X = Cl, Br, I) have gained recently for the use of solid-state batteries, and the idea that a softer, mo...

The lithium argyrodites Li6PS5X (X = Cl, Br, and I) have been gaining momentum as candidates for electrolytes in all-solid-state batteries. While these materials have been well-characterized struct...

Exploration of sulfidic sodium solid electrolytes and their design contributes to advances insolid state sodium batteries. Such design is guided by a better understanding of fast sodiumtransport, for instance in the herein studied Na11Sn2PS12-type materials. By using Rietveldrefinements against synchrotron X-ray diffraction and electrochemical impedancespectroscopy, the influence of aliovalent substitution onto the structure and transport inNa11+xSn2P1−xMxS12 with M = Ge and Sn is investigated. Whereas Sn induces strongerstructural changes than Ge, the found influence on the sodium sublattice and the ionic transportproperties are comparable. Overall, a reduced in-grain activation energy of Na+ transport canbe found with the reducing Na+ vacancy concentration. This work explores previouslyunreported phases in the Na11Sn2PS12 structure type that, based on their determined propertiesreveal Na+ vacancy concentrations to be an important factor guiding further understandingwithin Na11Sn2PS12-type materials