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Polycrystalline ion conductors are widely used as solid electrolytes in energy storage technologies. However, they often exhibit poor ion transport across grain boundaries and pores. This work demonstrates that strategically tuning the mesoscale microstructures, including pore size, pore distribution, and chemical compositions of grain boundaries, can improve ion transport. Using LiTa₂PO₈as a case study, we have shown that the combination of LiF as a sintering agent with Hf⁴⁺implantation improves grain-grain contact, resulting in smaller, evenly distributed pores, reduced chemical contrast, and minimized nonconductive impurities. A suite of techniques has been used to decouple the effects of LiF and Hf⁴⁺. Specifically, LiF modifies particle shape and breaks large pores into smaller ones, while Hf⁴⁺addresses the chemical mismatches between grains and grain boundaries. Consequently, this approach achieves nearly two orders of magnitude improvement in ion conduction. Tuning mesoscale structures offers a cost-effective method for enhancing ion transport in polycrystalline systems and has notable implications for synthesizing high-performance ionic materials. 

The Cl–S mixed-anion sublattice of Li_1.6AlCl_3.4S_0.6creates face- and edge-shared octahedra that connect to form 3D ion conduction pathways with low activation energy barriers. 

Li_3.6In₇S_11.8Cl has a face-centered cubic arrangement of S²⁻/Cl⁻stabilized by Li⁺/In³⁺that form 3D ion conduction paths. The moisture stability and fast ion conduction make Li_3.6In₇S_11.8Cl a promising electrolyte for solid-state batteries. 

Abstract All‐solid‐state potassium batteries emerge as promising alternatives to lithium batteries, leveraging their high natural abundance and cost‐effectiveness. Developing potassium solid electrolytes (SEs) with high room‐temperature ionic conductivity is critical for realizing efficient potassium batteries. In this study, we present the synthesis of K_2.98Sb_0.91S_3.53Cl_0.47, showcasing a room‐temperature ionic conductivity of 0.32 mS/cm and a low activation energy of 0.26 eV. This represents an increase of over two orders of magnitude compared to the parent compound K₃SbS₄, marking the highest reported ionic conductivity for non‐oxide potassium SEs. Solid‐state³⁹K magic‐angle‐spinning nuclear magnetic resonance on K_2.98Sb_0.91S_3.53Cl_0.47reveals an increased population of mobile K⁺ions with fast dynamics. Ab initio molecular dynamics (AIMD) simulations further confirm a delocalized K⁺density and significantly enhanced K⁺diffusion. This work demonstrates diversification of the anion sublattice as an effective approach to enhance ion transport and highlights K_2.98Sb_0.91S_3.53Cl_0.47as a promising SE for all‐solid‐state potassium batteries. 

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 Li_5.07PS_4.07(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. 

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 Li_3‐3yHo_1+yCl_6‐xBr_xachieves 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. Li_3‐3yHo_1+yCl_6‐xBr_xalso 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.