Optimizing NaF-Rich Solid Electrolyte Interphase for Stabilizing Sodium Metal Batteries by Electrolyte Additive

NaF-rich electrode-electrolyte interphases play crucial roles in determining the cycling stability of sodium metal batteries (SMBs) because of their electronic insulation and mechanical stability. In this work, perfluorobenzene (PFB) is proposed as the additive to contribute the formation of NaF-rich solid electrolyte interphases (SEI). PFB at the periphery of the solvation layer can pull out a part of the EC with the lowest solvation energy by Van der Waals forces, thus allowing more PF6- to participate in the Na+ solvation layer and form an anion-aggregated solvation sheath, thus promoting the decomposition of PF6- to produce NaF. In addition, PFB has a higher highest occupied molecular orbital and lower lowest unoccupied molecular orbital energy level, which also preferentially decomposes to produce NaF at both electrodes. Benefiting from the intensified NaF ratio in SEI, the Na||Na symmetric cells with such an electrolyte achieves a superior cycling life over 350 h at 1 mA cm(-2), and the Na||Na3V2(PO4)(2)O2F batteries also realize ultrahigh cycling performance with 88.8% capacity retention after 500 cycles.