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2LiX-GaF3(X = Cl, Br, I) electrolytes offer favorable features for solid-state batteries: mechanical pliability and high conductivities. However, understanding the origin of fast ion transport in 2LiX-GaF3has been challenging. The ionic conductivity order of 2LiCl-GaF3(3.20 mS/cm) > 2LiBr-GaF3(0.84 mS/cm) > 2LiI-GaF3(0.03 mS/cm) contradicts binary LiCl (10−12S/cm) < LiBr (10−10S/cm) < LiI (10−7S/cm). Using multinuclear7Li,71Ga,19F solid-state nuclear magnetic resonance and density functional theory simulations, we found that Ga(F,X)
n polyanions boost Li+-ion transport by weakening Li+-X−interactions via charge clustering. In 2LiBr-GaF3and 2LiI-GaF3, Ga-X coordination is reduced with decreased F participation, compared to 2LiCl-GaF3. These insights will inform electrolyte design based on charge clustering, applicable to various ion conductors. This strategy could prove effective for producing highly conductive multivalent cation conductors such as Ca2+and Mg2+, as charge clustering of carboxylates in proteins is found to decrease their binding to Ca2+and Mg2+. -
Abstract Polyanion rotations are often linked to cation diffusion, but the study of multiple polyanion systems is scarce due to the complexities in experimentally determining their dynamic interactions. This work focuses on BH4‐based argyrodites, synthesized to achieve a high conductivity of 11 mS cm−1. Advanced tools, including high‐resolution X‐ray diffraction, neutron pair distribution function analysis, and mutinuclear magic‐angle‐spinning nuclear magnetic resonance (NMR) spectroscopy and relaxometry, along with theoretical calculations, are employed to unravel the dynamic intricacies among the dual polyanion lattice and active charge carriers. The findings reveal that the anion sublattice of Li5.07PS4.07(BH4)1.93affords an even temporal distribution of Li among PS43−and BH4−, suggesting minimal trapping of the charge carriers. Moreover, the NMR relaxometry unveils rapid BH4−rotation on the order of ∼GHz, affecting the slower rotation of neighboring PS43−at ∼100 MHz. The PS43−rotation synchronizes with Li+motion and drives superionic transport. Thus, the PS43−and BH4−polyanions act as two‐staged dual motors, facilitating rapid Li+diffusion.
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Abstract Localized atomistic disorder in halide‐based solid electrolytes (SEs) can be leveraged to boost Li+mobility. In this study, Li+transport in structurally modified Li3HoCl6, via Br−introduction and Li+deficiency, is explored. The optimized Li3‐3
y Ho1+y Cl6‐x Brx achieves an ionic conductivity of 3.8 mS cm−1at 25 °C, the highest reported for holmium halide materials.6,7Li nuclear magnetic resonance and relaxometry investigations unveil enhanced ion dynamics with bromination, attaining a Li+motional rate neighboring 116 MHz. X‐ray diffraction analyses reveal mixed‐anion‐induced phase transitions with disproportionate octahedral expansions and distortions, creating Ho‐free planes with favorable energetics for Li+migration. Bond valence site energy analysis highlights preferred Li+transport pathways, particularly in structural planes devoid of Ho3+blocking effects. Molecular dynamics simulations corroborate enhanced Li+diffusion with Br−introduction into Li3HoCl6. Li‐Ho electrostatic repulsions in the (001) plane presumably drive Li+diffusion into the Ho‐free (002) layer, enabling rapid intraplanar Li+motion and exchange between the 2d and 4h sites. Li3‐3y Ho1+y Cl6‐x Brx also demonstrates good battery cycling stability. These findings offer valuable insights into the intricate correlations between structure and ion transport and will help guide the design of high‐performance fast ion conductors for all‐solid‐state batteries.