Fluorinated Aromatic Diluent for High‐Performance Lithium Metal Batteries

• Published in: Angewandte Chemie International Edition Vol. 59; no. 35; pp. 14869 - 14876
• Main Authors: Yoo, Dong‐Joo, Yang, Sungyun, Kim, Ki Jae, Choi, Jang Wook
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 24.08.2020
• Edition: International ed. in English
• Subjects: Aluminum; Aromatic compounds; dendrite growth; Electrolytes; Energy levels; Fluorides; fluorinated aromatic diluent; Fluorination; Fluorine; Lithium; Lithium fluoride; Lithium ions; lithium metal batteries; Metal concentrations; Molecular orbitals; Salts; solid electrolyte interphase; fluorinated aromatic diluent; solid electrolyte interphase; dendrite growth; electrolytes; lithium metal batteries
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202003663

In lithium metal batteries, electrolytes containing a high concentration of salts have demonstrated promising cyclability, but their practicality with respect to the cost of materials is yet to be proved. Here we report a fluorinated aromatic compound, namely 1,2‐difluorobenzene, for use as a diluent solvent in the electrolyte to realize the “high‐concentration effect”. The low energy level of the lowest unoccupied molecular orbital (LUMO), weak binding affinity for lithium ions, and high fluorine‐donating power of 1,2‐difluorobenzene jointly give rise to the high‐concentration effect at a bulk salt concentration near 2 m, while modifying the composition of the solid‐electrolyte‐interphase (SEI) layer to be rich in lithium fluoride (LiF). The employment of triple salts to prevent corrosion of the aluminum current collector further improves cycling performance. This study offers a design principle for achieving a local high‐concentration effect with reasonably low bulk concentrations of salts. 1,2‐Difluorobenzene serves as an electrolyte diluent to realize the high‐concentration effect in lithium metal batteries even at a bulk salt concentration near 2 m. The incorporation of this diluent also induces an anion‐associated lithium solvation structure to passivate lithium metal with a LiF‐rich solid‐electrolyte‐interphase (SEI) layer, thereby resulting in superior cyclability.