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The performance of all‐solid‐state batteries (ASSBs) relies on the Li⁺transport and stability characteristics of solid electrolytes (SEs). Li₃PS₄is notable for its stability against lithium metal, yet its ionic conductivity remains a limiting factor. This study leverages local structural disorder via O substitution to achieve an ionic conductivity of 1.38 mS cm⁻¹with an activation energy of 0.34 eV for Li₃PS_4−xO_x(x = 0.31). Optimal O substitution transforms Li⁺transport from 2D to 3D pathways with increased ion mobility. Li₃PS_3.69O_0.31exhibits improvements in the critical current density and stability against Li metal and retains its electrochemical stability window compared with Li₃PS₄. The practical implementation of Li₃PS_3.69O_0.31in ASSBs half‐cells, particularly when coupled with TiS₂as the cathode active material, demonstrates substantially enhanced capacity and rate performance. This work elucidates the utility of introducing local structural disorder to ameliorate SE properties and highlights the benefits of strategically combining the inherent strengths of sulfides and oxides via creating oxysulfide SEs.

To enhance Li⁺transport in all‐solid‐state batteries (ASSBs), harnessing localized nanoscale disorder can be instrumental, especially in sulfide‐based solid electrolytes (SEs). In this investigation, the transformation of the model SE, Li₃PS₄, is delved into via the introduction of LiBr.³¹P nuclear magnetic resonance (NMR)unveils the emergence of a glassy PS₄³⁻network interspersed with Br⁻.⁶Li NMR corroborates swift Li⁺migration between PS₄³⁻and Br⁻, with increased Li⁺mobility indicated by NMR relaxation measurements. A more than fourfold enhancement in ionic conductivity is observed upon LiBr incorporation into Li₃PS₄. Moreover, a notable decrease in activation energy underscores the pivotal role of Br⁻incorporation within the anionic lattice, effectively reducing the energy barrier for ion conduction and transitioning Li⁺transport dimensionality from 2D to 3D. The compatibility of Li₃PS₄with Li metal is improved through LiBr incorporation, alongside an increase in critical current density from 0.34 to 0.50 mA cm⁻², while preserving the electrochemical stability window. ASSBs with 3Li₃PS₄:LiBr as the SE  showcase robust high‐rate and long‐term cycling performance. These findings collectively indicate the potential of lithium halide incorporation as a promising avenue to enhance the ionic conductivity and stability of SEs.

The correlation between lattice chemistry and cation migration in high‐entropy Li⁺conductors is not fully understood due to challenges in characterizing anion disorder. To address this issue, argyrodite family of Li⁺conductors, which enables structural engineering of the anion lattice, is investigated. Specifically, new argyrodites, Li_5.3PS_4.3Cl_1.7−xBr_x(0 ≤x≤ 1.7), with varying anion entropy are synthesized and X‐ray diffraction, neutron scattering, and multinuclear high‐resolution solid‐state nuclear magnetic resonance (NMR) are used to determine the resulting structures. Ion and lattice dynamics are determined using variable‐temperature multinuclear NMR relaxometry and maximum entropy method analysis of neutron scattering, aided by constrained ab initio molecular dynamics calculations. 15 atomic configurations of anion arrangements are identified, producing a wide range of local lattice dynamics. High entropy in the lattice structure, composition, and dynamics stabilize otherwise metastable Li‐deficient structures and flatten the energy landscape for cation migration. This resulted in the highest room‐temperature ionic conductivity of 26 mS cm⁻¹and a low activation energy of 0.155 eV realized in Li_5.3PS_4.3Cl_0.7Br, where anion disorder is maximized. This study sheds light on the complex structure–property relationships of high‐entropy superionic conductors, highlighting the significance of heterogeneity in lattice dynamics.

Lattice oxygen redox yields anomalous capacity and can significantly increase the energy density of layered Li‐rich transition metal oxide cathodes, garnering tremendous interest. However, the mechanism behind O redox in these cathode materials is still under debate, in part due to the challenges in directly observing O and following associated changes upon electrochemical cycling. Here, with¹⁷O NMR as a direct probe of O activities, it is demonstrated that stacking faults enhance O redox participation compared with Li₂MnO₃domains without stacking faults. This work is concluded by combining both ex situ and in situ¹⁷O NMR to investigate the evolution of O at 4i, 8j sites from monoclinicC2/mand 6c(1), 6c(2), 6c(3) sites from the stacking faults (P3₁12). These measurements are further corroborated and explained by first‐principles calculations finding a stabilization effect of stacking faults in delithiated Li₂MnO₃. In situ¹⁷O NMR tracks O activities with temporal resolution and provides a quantitative determination of reversible O redox versus irreversible processes that form short covalent OO bonds. This work provides valuable insights into the O redox reactions in Li‐excess layered cathodes, which may inspire new material design for cathodes with high specific capacity.

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)_npolyanions 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⁺.