Anion-Tuned Fluorinated Solvation Sheath Enables Stable Lithium Metal Batteries

Continuous side reactions between conventional carbonate-based electrolytes and electrodes lead to electrolyte consumption and the growth of lithium dendrites, which always lead to serious capacity fading or safety issues, hindering the development of lithium metal batteries. Here, a nonflammable all-fluorinated electrolyte with the anion-participating Li⁺ solvation sheath is developed and the corresponding electrochemical properties are studied. Combining theoretical calculations and X-ray photoelectron spectroscopy analysis, ethyl 2,2,2-trifluoroethyl carbonate (ETFEC) and methyl difluoroacetate (MDFA) as cosolvents in the all-fluorinated electrolyte, PF₆^- anions accumulate on the lithium metal anode and preferentially reduced to obtain a LiF-rich solid electrolyte layer, inducing uniform lithium metal deposition. Additionally, the anions located in the solvation structure improve the reduction stability of the solvent, which avoids the rapid decline in battery capacity caused by the continued decomposition of the solvent. Consequently, The Li||NCM811 battery achieved initial capacity retention of 71.48% after 430 cycles at a voltage of 4.3 V, and the capacity retention reached 64.52% after 225 cycles even at a high voltage of 4.5 V. This nonflammable electrolyte can alleviate the rapid decline in battery capacity caused by solvent decomposition.