All-fluorinated electrolyte directly tuned Li+ solvation sheath enabling high-quality passivated interfaces for robust Li metal battery under high voltage operation

Highly fluorinated electrolytes are appealing to directly improve the evolution of Li+ solvation sheath and arouse high-quality solid-electrolyte interphases (SEIs) for Li metal batteries (LMBs) with stable cycling. Herein, the effect of fluorinated engineering-based electrolytes on Li+ solvation structure and the relevant electrochemical performance were systematically investigated. By a selective combination of the ethylene carbonate (EC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), and ethyl (2,2,2-trifluoroethyl) carbonate (ETFEC), it is found that all-fluorinated electrolyte containing FEC and ETFEC directly optimizes the Li+ solvation environments where coordination numbers of Li+ decreases from 3.75 in none-fluorinated electrolyte to 3.02 in all-fluorinated electrolyte according to molecular dynamic (MD) simulations. Impressively, fast Li+ desolvation in allfluorinated electrolyte induced stable LiF-rich interface accompanied by the inhibition of Li dendrites, and thus Li||Cu asymmetrical cells achieved high CE of average 98.3% at 0.5 mA cm-2 as well as superior cycling stability. Encouragingly, the Li||NCM811 cells even retained the initial capacity of 72.3% with an average CE of 99.8% at high voltage (up to 4.6 V) after 225 cycles. This work offers a Li+ solvation sheath-directly tuned strategy to construct the ideal interface chemistry for high-performance LMBs.