Skeletal editing of ether-based electrolyte diluents by oxygen-distal fluorination for energy-dense Li metal battery

Enhancing cycling reversibility in high-energy-density lithium metal batteries necessitates precise management of electrolyte-derived electrochemical reactions at electrodes and interphases, yet recently developed localized high-concentration electrolytes suffer from limited tunability of these reactions for the non-solvation-participating nature of oxygen-proximal fluorinated diluents. Here we address this issue by synthesizing an oxygen-distal fluorinated di-2,2,3,3-tetrafluoropropoxyethane diluent whose molecular skeleton is strategically edited to position fluorine atoms distal to oxygen centers that attenuate electron-withdrawing effects at Li+-coordination sites, enabling: enhanced diluent/anion participation and reduced volatile solvents in solvation shells; atypical H-F bonding between diluent and solvent toward enhanced oxidation resistance; and promotion of diluent and salt-derived highly stable inorganic-rich interphase formation. This electrolyte achieves 99.8% Li plating/stripping Coulombic efficiency, 450 stable cycles in 4.5 V high-voltage Li || LiNi0.8Mn0.1Co0.1O2 cells, and 5.9-Ah, 504.6 Wh kg–1 (based on mass of all components including packaging) pouch cells that exhibits 0.053% per-cycle capacity decay. This work introduces oxygen-distal fluorination as a potential molecular skeleton editing strategy for stable energy-dense lithium metal batteries. Overcoming parasitic reactions between the electrolyte and electrodes is essential for realizing energy-dense lithium metal batteries. Here, the authors develop an oxygen distal fluorinated diluent that promotes a diluent- and anion-rich solvation structure, forming a stable inorganic-rich interphase and stable cycling in pouch cells at 500 Wh kg–1 level.