From Cation Solvation to Anion Coordination: Lewis-Acidic Boranes Enable Halide Salt Electrolytes

Ion solvation in battery electrolytes involves supramolecular host-guest interactions and is most often enabled by Lewis basic coordination of cations, sometimes at the expense of cation mobility. Here, we investigate anion-centered solvation using Lewis acidic supramolecular hosts. We introduce a class of small-molecule boranes that selectively coordinate anions, enabling systematic interrogation of how anion binding strength governs salt dissociation and ion transport. A family of readily accessible boranes spanning a wide range of Lewis acidities was synthesized and evaluated with Li- and Na-based salts. Increasing borane Lewis acidity strongly correlated with enhanced dissociation and ionic conductivity of otherwise poorly soluble halide salts (Cl^-, F^-), yielding order-of-magnitude conductivity enhancements and, in some cases, performance exceeding that of TFSI-based electrolytes. These results establish anion coordination strength as a powerful and tunable handle for regulating ion transport and expand supramolecular host-guest chemistry to the rational design of electrolyte solvation environments.