Anion-Regulated Weakly Solvating Electrolytes for High-Voltage Lithium Metal Batteries

Abstract

Development of advanced high-voltage electrolytes is key to achieving high-energy-density lithium metal batteries (LMBs). Weakly solvating electrolytes (WSE) can produce unique anion-driven interphasial chemistry via altering the solvating power of the solvent, but it is difficult to dissolve the majority of Li salts and fail to cycle at a cut-off voltage above 4.5 V. Herein, we present a new-type WSE that is regulated by the anion rather than the solvent, and the first realize stable cycling of dimethoxyethane (DME) at 4.6 V without the use of the “solvent-in-salt” strategy. The relationships between the degree of dissociation of salts, the solvation structure of electrolytes, and the electrochemical performance of LMBs were systematically investigated. We found that LiBF4, which has the lowest degree of dissociation, can construct an anion-rich inner solvation shell, resulting in anion-derived anode/cathode interphases. Thanks to such unusual solvation structure and interphasial chemistry, the Li-LiCoO2 full cell with LiBF4-based WSE could deliver excellent rate performance (115 mAh g−1 at 10 C) and outstanding cycling stability even under practical conditions, including high loading (10.7 mg cm−2), thin Li (50 μm), and limited electrolyte (1.2 μL mg−1).