Ionic Conductivity and Its Dependence on Structural Disorder in Halogenated Argyrodites Li<sub>6</sub>PS<sub>5</sub>X (X = Br, Cl, I)

Stamminger, Andreas R.; Ziebarth, Benedikt; Mrovec, Matous; Hammerschmidt, Thomas; Drautz, Ralf

doi:10.1021/acs.chemmater.9b02047

Cited by 53 publications

(66 citation statements)

References 59 publications

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“…This systematically decreasing lattice parameter with increasing synthesis temperature is significant and not expected. Whereas the difference in the ionic radii between the halide and the sulfide anion has been shown to affect the lattice volume in argyrodites significantly, [ 4,15,25–28 ] here no changes in composition are present that could explain this behavior. To understand this relationship, the influence of the site‐disorder needs to be explored.…”

Section: Resultsmentioning

confidence: 99%

Engineering the Site‐Disorder and Lithium Distribution in the Lithium Superionic Argyrodite Li₆PS₅Br

Gautam

Sadowski

Ghidiu

et al. 2020

Advanced Energy Materials

141

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Lithium argyrodite superionic conductors, of the form Li6PS5X (X = Cl, Br, and I), have shown great promise as electrolytes for all‐solid‐state batteries because of their high ionic conductivity and processability. The ionic conductivity of these materials is highly influenced by the structural disorder of S2−/X− anions; however, it is unclear if and how this affects the Li distribution and how it relates to transport, which is critical for improving conductivities. Here it is shown that the site‐disorder once thought to be inherent to given compositions can be carefully controlled in Li6PS5Br by tuning synthesis conditions. The site‐disorder increases with temperature and can be “frozen” in. Neutron diffraction shows this phenomenon to affect the Li+ substructure by decreasing the jump distance between so‐called “cages” of clustered Li+ ions; expansion of these cages makes a more interconnected pathway for Li+ diffusion, thereby increasing ionic conductivity. Additionally, ab initio molecular dynamics simulations provide Li+ diffusion coefficients and time‐averaged radial distribution functions as a function of the site‐disorder, corroborating the experimental results on Li+ distribution and transport. These approaches of modulating the Li+ substructure can be considered essential for the design and optimization of argyrodites and may be extended to other lithium superionic conductors.

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Section: Resultsmentioning

confidence: 99%

Engineering the Site‐Disorder and Lithium Distribution in the Lithium Superionic Argyrodite Li₆PS₅Br

Gautam

Sadowski

Ghidiu

et al. 2020

Advanced Energy Materials

141

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“…In Li 6 PS 5 Cl and Li 6 PS 5 Br, the S and Cl, or S and Br, atoms are substitutionally disordered, which has been attributed to their similar ionic radii 11 , 24 , 28 giving a low formation energy for S/X antisites. 29 , 30 Molecular dynamics simulations of Li 6 PS 5 X in which the degree of S/X disorder has been systematically varied provide additional evidence for a causal link between anion substitutional disorder and fast lithium-ion transport. 22 , 30 − 34…”

Section: Introductionmentioning

confidence: 99%

“… 29 , 30 Molecular dynamics simulations of Li 6 PS 5 X in which the degree of S/X disorder has been systematically varied provide additional evidence for a causal link between anion substitutional disorder and fast lithium-ion transport. 22 , 30 − 34…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li₆PS₅X Argyrodites

Morgan

2021

Chem. Mater.

112

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The rational development of fast-ion-conducting solid electrolytes for all-solid-state lithium-ion batteries requires understanding the key structural and chemical principles that give some materials their exceptional ionic conductivities. For the lithium argyrodites Li 6 PS 5 X (X = Cl, Br, or I), the choice of the halide, X, strongly affects the ionic conductivity, giving room-temperature ionic conductivities for X = {Cl,Br} that are ×10 3 higher than for X = I. This variation has been attributed to differing degrees of S/X anion disorder. For X = {Cl,Br}, the S/X anions are substitutionally disordered, while for X = I, the anion substructure is fully ordered. To better understand the role of substitutional anion disorder in enabling fast lithium-ion transport, we have performed a first-principles molecular dynamics study of Li 6 PS 5 I and Li 6 PS 5 Cl with varying amounts of S/X anion-site disorder. By considering the S/X anions as a tetrahedrally close-packed substructure, we identify three partially occupied lithium sites that define a contiguous three-dimensional network of face-sharing tetrahedra. The active lithium-ion diffusion pathways within this network are found to depend on the S/X anion configuration. For anion-disordered systems, the active site–site pathways give a percolating three-dimensional diffusion network; whereas for anion-ordered systems, critical site–site pathways are inactive, giving a disconnected diffusion network with lithium motion restricted to local orbits around S positions. Analysis of the lithium substructure and dynamics in terms of the lithium coordination around each sulfur site highlights a mechanistic link between substitutional anion disorder and lithium disorder. In anion-ordered systems, the lithium ions are pseudo-ordered, with preferential 6-fold coordination of sulfur sites. Long-ranged lithium diffusion would disrupt this SLi 6 pseudo-ordering, and is, therefore, disfavored. In anion-disordered systems, the pseudo-ordered 6-fold S–Li coordination is frustrated because of Li–Li Coulombic repulsion. Lithium positions become disordered, giving a range of S–Li coordination environments. Long-ranged lithium diffusion is now possible with no net change in S–Li coordination numbers. This gives rise to superionic lithium transport in the anion-disordered systems, effected by a concerted string-like diffusion mechanism.

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“…36 The origin of this anion-site-disorder has not been unequivocally resolved, but theoretical and experimental analyses suggest that anion mixing is facilitated by the similar ionic radii for S 2− versus Br − or Cl − . 9,37 The absence or presence of site-disorder in Li6PS5X argyrodites strongly affects their lithium transport properties. Li6PS5I…”

Section: Introductionmentioning

confidence: 99%

Local Charge Inhomogeneity and Lithium Distribution in the Superionic Argyrodites Li₆PS₅X (X = Cl, Br, I)

et al. 2020

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The lithium-argyrodites Li 6 PS 5 X (X = Cl, Br, I) exhibit high lithium-ion conductivities, making them promising candidates for use in solid-state batteries. These solid electrolytes can show considerable substitutional X − /S 2− anion-disorder, with greater disorder typically correlated with higher lithium-ion conductivities. The atomic-scale effects of this anion site-disorder within the host lattice-in particular how lattice disorder modulates the lithium substructure-are not well understood. Here, we characterize the lithium substructure in Li 6 PS 5 X (X = Cl, Br, I) as a function of temperature and anion site-disorder, using Rietveld refinements against temperature-dependent neutron diffraction data. Analysis of these high-resolution diffraction data reveals an additional lithium position previously unreported for Li 6 PS 5 Xargyrodites, suggesting that the lithium conduction pathway in these materials differs from the most common model proposed in earlier studies. Analysis of the Li + positions and their radial distributions reveals that greater inhomogeneityof the local anionic charge, due to X − /S 2− site-disorder, is associated with more spatially-diffuse lithium distributions. This observed coupling of site-disorder and lithium distribution provides a possible explanation for the enhanced lithium transport in anion-disordered lithium argyrodites, and highlights the complex interplay between anion configuration and lithium substructure in this family of superionic conductors. File list (2) download file view on ChemRxiv revised manuscript.pdf (2.52 MiB) download file view on ChemRxiv Revised Supporting Information.pdf (1.35 MiB)

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Ionic Conductivity and Its Dependence on Structural Disorder in Halogenated Argyrodites Li₆PS₅X (X = Br, Cl, I)

Cited by 53 publications

References 59 publications

Engineering the Site‐Disorder and Lithium Distribution in the Lithium Superionic Argyrodite Li₆PS₅Br

Engineering the Site‐Disorder and Lithium Distribution in the Lithium Superionic Argyrodite Li₆PS₅Br

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li₆PS₅X Argyrodites

Local Charge Inhomogeneity and Lithium Distribution in the Superionic Argyrodites Li₆PS₅X (X = Cl, Br, I)

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Ionic Conductivity and Its Dependence on Structural Disorder in Halogenated Argyrodites Li6PS5X (X = Br, Cl, I)

Cited by 53 publications

References 59 publications

Engineering the Site‐Disorder and Lithium Distribution in the Lithium Superionic Argyrodite Li6PS5Br

Engineering the Site‐Disorder and Lithium Distribution in the Lithium Superionic Argyrodite Li6PS5Br

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li6PS5X Argyrodites

Local Charge Inhomogeneity and Lithium Distribution in the Superionic Argyrodites Li6PS5X (X = Cl, Br, I)

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Ionic Conductivity and Its Dependence on Structural Disorder in Halogenated Argyrodites Li₆PS₅X (X = Br, Cl, I)

Engineering the Site‐Disorder and Lithium Distribution in the Lithium Superionic Argyrodite Li₆PS₅Br

Engineering the Site‐Disorder and Lithium Distribution in the Lithium Superionic Argyrodite Li₆PS₅Br

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li₆PS₅X Argyrodites

Local Charge Inhomogeneity and Lithium Distribution in the Superionic Argyrodites Li₆PS₅X (X = Cl, Br, I)