A Universal Class of Cubic Crystalline Alkali Organic-Inorganic Glyme-Based Halides

Halide salts have played a central role in lithium-ion battery development as components of liquid, polymer, ionic-liquid, and solid-state electrolytes, yet their high solubility has limited their exploration as electrode materials. Here, we demonstrate a universal self-assembly reaction between halide solid electrolytes and glyme-based solvents that produces a new family of alkali glyme-based halides, ABX6·mGn (A = Li, Na, K; B = Ta, Nb; X = Cl, Br; Gn = mono- to tetraglyme; m = number of Gn). They have a cubic structure similar to CsCl, with alkali cations at the center surrounded by fast-moving glyme molecules and BX6 octahedra at the corners. We demonstrated that, upon heating, these solvent-separated ion pair (SSIP) structures can transform into contact ion pair (CIP) phases, as shown for KTaCl6·1G4 with infinite 1D chain motifs. Combined thermal, EPR, and NMR measurements together with DFT studies were used to gain insight into charge distribution, glyme conformation, and rotation in order to rationalize their formation mechanism and solvation structures. Additionally, we found that the ionic conductivity of these solids is low (10-7-10-4 mS/cm). However, it increases to 1-10 mS/cm in the liquid state. K-based systems demonstrate the highest conductivity in both states. Furthermore, our electrochemical and in situ XRD investigations of KTaCl6 in potassium-ion cells with glyme-based electrolytes reveal that displacement and insertion reactions occur through low-voltage polarization via the formation of K2TaCl6. Our work advances the understanding of glyme-based halide complexes, paving the way for rich chemistry with potential applications in solid-state ionics and beyond.