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 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