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.

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.

The frequency-dependent capacitance of low-temperature solution-processed metal oxide (MO) dielectrics typically yields unreliable and unstable thin-film transistor (TFT) performance metrics, which hinders the development of next-generation roll-to-roll MO electronics and obscures intercomparisons between processing methodologies. Here, capacitance values stable over a wide frequency range are achieved in low-temperature combustion-synthesized aluminum oxide (AlO x ) dielectric films by fluoride doping. For an optimal F incorporation of ∼3.7 atomic % F, the F:AlO x film capacitance of 166 ± 11 nF/cm2 is stable over a 10–1–104 Hz frequency range, far more stable than that of neat AlO x films (capacitance = 336 ± 201 nF/cm2) which falls from 781 ± 85 nF/cm2 to 104 ± 4 nF/cm2 over this frequency range. Importantly, both n-type/inorganic and p-type/organic TFTs exhibit reliable electrical characteristics with minimum hysteresis when employing the F:AlO x dielectric with ∼3.7 atomic % F. Systematic characterization of film microstructural/compositional and electronic/dielectric properties by X-ray photoelectron spectroscopy, time-of-fight secondary ion mass spectrometry, cross-section transmission electron microscopy, solid-state nuclear magnetic resonance, and UV–vis absorption spectroscopy reveal that fluoride doping generates AlOF, which strongly reduces the mobile hydrogen content, suppressing polarization mechanisms at low frequencies. Thus, this work provides a broadly applicable anion doping strategy for the realization of high-performance solution-processed metal oxide dielectrics for both organic and inorganic electronics applications.

No abstract