No abstract

Argyrodites, with fast lithium-ion conduction, are promising for applications in rechargeable solid-state lithium-ion batteries. We report a new compositional space of argyrodite superionic conductors, Li 6−x PS 5−x ClBr x [0 ≤ x ≤ 0.8], with a remarkably high ionic conductivity of 24 mS/cm at 25 °C for Li 5.3 PS 4.3 ClBr 0.7 . In addition, the extremely low lithium migration barrier of 0.155 eV makes Li 5.3 PS 4.3 ClBr 0.7 highly promising for low-temperature operation. Average and local structure analyses reveal that bromination (x > 0) leads to (i) retention of the parent Li 6 PS 5 Cl structure for a wide range of x in Li 6−x PS 5−x ClBr x (0 ≤ x ≤ 0.7), (ii) co-occupancy of Cl − , Br − , and S 2− at 4a/4d sites, and (iii) gradually increased Li + -ion dynamics, eventually yielding a "liquid-like" Li-sublattice with a flattened energy landscape when x approaches 0.7. In addition, the diversity of anion species and Li-deficiency in halogen-rich Li 6−x PS 5−x ClBr x induce hypercoordination and coordination entropy for the Li-sublattice, also leading to enhanced Li + -ion transport in Li 6−x PS 5−x ClBr x . This study demonstrates that mixed-anion framework can help stabilize highly conductive structures in a compositional space otherwise unstable with lower anion diversity.

No abstract

High ionic conductivity of solid electrolytes is key to achieving high-power all-solid-state rechargeable batteries. The superionic argyrodite family is among the most conductive Li-ion conductors. However, their potential in ionic conductivity and stability is far from being reached, especially with Li 6 PS 5 Br. Here, we synthesized Li 6−x PS 5−x Br 1+x with increased site mixing of Br − /S 2− . An ionic conductivity of 11 mS cm −1 at 25 °C is achieved with a low activation energy of 0.18 eV for Li 5.3 PS 4.3 Br 1.7 . The influence of Br − /S 2− mixing on ion conduction is systematically investigated with multinuclear solid-state NMR coupled with X-ray diffraction and impedance spectroscopy. A statistically random distribution of Br − and S 2− at 4d sites is observed with 31 P NMR. The resulting local structures regulate the jump rates of their neighboring Li ions and Li redistribution. As a result, the increased Li + occupancy at 24g sites promotes fast ion conduction, and the role of Li (24g) in ion conduction has been elucidated with tracer-exchange NMR. Experimental evidence combined with density functional theory calculations has revealed that the particular arrangement of 1S3Br at 4d sites near Li maximizes overall Li + conduction. This insight applies to other argyrodites and will be useful to the design of new fast ion conductors.

It is determined with isotope-replacement NMR that Li ions transport via TEGDME-containing phases in a representative composite electrolyte LLZO–PEO–TEGDME.