Correlating Structural Disorder to Li⁺ Ion Transport in Li_4–xGe_1–xSb_xS₄ (0 ≤ x ≤ 0.2)

Abstract

Strong compositional influences are known to affect the ionic transport within the thio-LISICON family; however, a deeper understanding of the resulting structure–transport correlations has up until now been lacking. Employing a combination of high-resolution neutron diffraction, impedance spectroscopy, and nuclear magnetic resonance spectroscopy, together with bond valence site energy calculations and the maximum entropy method for determining the underlying Li+ scattering density distribution of a crystal structure, this work assesses the impact of the Li+ substructure and charge carrier density on the ionic transport within the Li4–x Ge1–x Sb x S4 substitution series. By incorporating Sb5+ into Li4GeS4, an anisometric expansion of the unit cell is observed. An additional Li+ position is found as soon as (SbS4)3– polyhedra are present, leading to a better local polyhedral connectivity and a higher disorder in the Li+ substructure. Here, we are able to relate structural disorder to an increase in configurational entropy, together with a 2 order-of-magnitude increase in ionic conductivity. This result reinforces the typically believed paradigm that structural disorder leads to improvements in ionic transport.

Enhanced Li-Ion Conductivity and Air Stability of Sb-Substituted Li4GeS4 toward All-Solid-State Li-Ion Batteries

“…In this work, Sb 5+ was chosen to substitute Ge 4+ in the structure of Li 4 GeS 4 to form a series of solid solutions Li 4– x Ge 1– x Sb x S 4 (0 ≤ x ≤ 0.75), which can induce Li-ion vacancies and facilitate Li-ion diffusion. ,,, Evolution of the crystal structure, ionic conductivity, and diffusion barrier energy in the series were investigated using the powder X-ray Rietveld refinement, ionic conductivity measurements, and bond valence site energy (BVSE) calculations. In the course of the present work, Helm et al reported the same substitution series with x values up to 0.2; in that study, the highest ionic conductivity was found for x = 0.09, showing 2.2 × 10 –5 S cm –1 at room temperature . In our case, we prepared phases with an extended substitution level up to x = 0.75 and obtained an order of magnitude higher ionic conductivity of 1.23 × 10 –4 S cm –1 for Li 3.68 Ge 0.69 Sb 0.31 S 4 (LGSbS-04), a material that also showed an enhanced air stability [a relative humidity (R.H.) of 15% at 303 K] compared to Li 3 PS 4 .…”

“…The Rietveld refinement results for the phases of x = 0.1, 0.25, and 0.333 are shown in the Supporting Information (Figures S8–S10 and Tables S2–S4). Recently, Helm et al found an additional lithium site [Li(4)] when Sb was substituted for Ge, which was confirmed by neutron diffraction . However, due to the low scattering power of Li atoms in XRD, which was only available under our circumstances, refinement including the Li(4) site was unstable in the present work.…”

“…4)] when Sb was substituted for Ge, which was confirmed by neutron diffraction. 40 However, due to the low scattering power of Li atoms in XRD, which was only available under our circumstances, refinement including the Li(4) site was unstable in the present work. Hence, only the three Li sites were considered in our refinement, where Li1 and Li3 were fully occupied, and Li2 was partially occupied.…”

“…In the course of the present work, Helm et al reported the same substitution series with x values up to 0.2; in that study, the highest ionic conductivity was found for x = 0.09, showing 2.2 × 10 −5 S cm −1 at room temperature. 40 In our case, we prepared phases with an extended substitution level up to x = 0.75 and obtained an order of magnitude higher ionic conductivity of 1.23 × 10 −4 S cm −1 for Li 3.68 Ge 0.69 Sb 0.31 S 4 (LGSbS-04), a material that also showed an enhanced air stability [a relative humidity (R.H.) of 15% at 303 K] compared to Li 3 PS 4 . The electrochemical oxidation stability of LGSbS-04 and the galvanostatic charge/discharge cycle performance of a battery cell with LGSbS-04 as the SE were studied using homemade press cells.…”

Trendbericht Festkörperchemie 2023

“…Demnach steigern die durch den Einbau bedingten Strukturänderungen die Konfigurationsentropie und damit auch die ionische Leitfähigkeit um bis zu zwei Größenordnungen (2,4 × 10 -7 S•cm -1 für Li 4 [GeS 4 ], 2,2 × 10 -5 S•cm -1 für Li 3,91 Ge 0,91 Sb 0,09 S 4 ). 2) Fässler, van Wüllen und Mitarbeitende berichteten über drei neue Hochtemperaturmodifikatio-nen der Lithiumphosphidotrielate ω-Li 9 [TrP 4 ] (Tr Al, Ga, In), die Li + -Ionenleitfähigkeiten von bis zu 4,5 mS • cm -1 bei Raumtemperatur zeigen (Abbildung 1). 3) Durch Experimente und quantenchemische Methoden erklären sie diese Beobachtung und korrelieren die Leitfähigkeit mit der Struktur.…”