Hitherto Unknown Solvent and Anion Pairs in Solvation Structures Reveal New Insights into High-Performance Lithium-Ion Batteries

Solvent-solvent and solvent-anion pairings in battery electrolytes have been identified for the first time by nuclear magnetic resonance spectroscopy. These hitherto unknown interactions are enabled by the hydrogen bonding induced by the strong Lewis acid Li⁺, and exist between the electron-deficient hydrogen (δ⁺H) present in the solvent molecules and either other solvent molecules or negatively-charged anions. Complementary with the well-established strong but short-ranged Coulombic interactions between cation and solvent molecules, such weaker but longer-ranged hydrogen-bonding casts the formation of an extended liquid structure in electrolytes that is influenced by their components (solvents, additives, salts, and concentration), which in turn dictates the ion transport within bulk electrolytes and across the electrolyte-electrode interfaces. The discovery of this new inter-component force completes the picture of how electrolyte components interact and arrange themselves, sets the foundation to design better electrolytes on the fundamental level, and probes battery performances.