High‐Safety Electrolytes with an Anion‐Rich Solvation Structure Tuned by Difluorinated Cations for High‐Voltage Lithium Metal Batteries

Abstract As next‐generation energy storage devices, lithium metal batteries (LMBs) must offer high safety, high‐voltage resistance, and a long life span. Electrolyte engineering is a facile strategy to tailor the interfacial chemistry of LMBs. In particular, the solvation structure and derived solid electrolyte interphase (SEI) are crucial for a satisfactory battery performance. Herein, a novel middle‐concentrated ionic liquid electrolyte (MCILE) with an anion‐rich solvation structure tuned by difluorinated cations is demonstrated to achieve ultrahigh safety, high‐voltage stability, and excellent ternary‐cathode compatibility. Novel gem‐difluorinated cations first synthesized for prestoring fluorine on positively charged species, not only preferentially adsorb in the inner‐Helmholtz layers, but also participate in regulating the Li + solvation structure, resulting in a robust interphase. Moreover, these weak interactions in the Li + solvation structure including anion–solvent and ionic liquid (IL) cation–solvent pairs are first revealed, which are beneficial for promoting an anion‐dominated solvation structure and the desolvation process. Benefiting from the unique anion‐rich solvation structure, a stable hetero‐SEI structure is obtained. The designed MCILE exhibits compatibility with Li metal anode and the high‐voltage ternary cathode at high temperatures (60 °C). This work provides a new approach for regulating the solvation structure and electrode interphase chemistry of LMBs via difluorinated IL cations.