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

As next-generation energy storage devices, lithium metal batteries (LMBs) must offer high safety, high-voltage resistance and a long lifespan. Electrolyte engineering is a facile yet effective 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 ultra-high without thermal runaway, high-voltage stability, high-temperature stability and excellent ternary-cathode compatibility. Novel gem-difluorinated cations firstly synthesised 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 anions-solvents and ionic liquids (IL) cations-solvents pairs are firstly revealed via two-dimensional nuclear magnetic resonance (2D NMR) in the bulk electrolyte, which are beneficial for promoting an anion-dominated solvation structure and the desolvation process demonstrated by theoretical calculation. Benefiting from the unique anion-rich solvation structure, a stable hetero SEI structure with a fluorine-rich mixed outer layer and an inorganic inner layer is obtained. The designed MCILE exhibits compatibility with Li metal anode and the high-voltage ternary-cathode at high temperatures (60 °C) and high voltages (4.5 V). This work provides a new approach for regulating the solvation structure and electrode interphase chemistry of LMBs via difluorinated IL cations. This article is protected by copyright. All rights reserved.