Perfluorinated Sulfonyl Fluoride Mediated Solvation and Interphase Dual Engineering in a Weakly‐Solvating Electrolyte for High‐Voltage Li‐Metal Pouch Cell

Abstract

The practical deployment of high‐voltage Ni‐rich lithium‐metal batteries is hindered by severe electrolyte decomposition at both electrodes. Herein, we design a weakly‐solvating electrolyte (WSE) with fluoroethylene carbonate (FEC) and 2,2,2‐trifluoroethyl methyl carbonate (FEMC) as solvents. This electrolyte promotes an anion‐dominated solvation sheath and forms inorganic‐rich interphases (LiF, Li2CO3, and LixPOyFz), yet these species remain largely confined to the surface, leaving inner layers rich in organic decomposition products. To address this, we introduce 3 wt% nonafluorobutanesulfonyl fluoride (NFBSF) as a multifunctional additive (WSE‐3SF). Combined theoretical and experimental analyses reveal that NFBSF does not coordinate Li+. Instead, it preferentially interacts with FEMC, creating a local low‐polarity environment that enhances PF6− incorporation into the solvation shell. This tailored solvation, together with direct NFBSF decomposition via selective S‐C/S‐F bond cleavage, yields robust interphases uniformly enriched in LiF, LiPO2F2, and sulfonate/sulfonyl fluoride species. Moreover, WSE‐3SF imparts improved physicochemical properties to the electrolyte. Consequently, the Li||Cu cell delivers a Coulombic efficiency of 98.5%, 5 V‐class Li||LiNi0.5Mn1.5O4 cell maintains cycling over 1000 cycles, and 4.5 V‐class 4.2 Ah Li||LiNi0.88Co0.07Mn0.05O2 pouch cell retains 96.3% capacity after 95 cycles. This work establishes a synergy between weakly solvating solvents and a purpose‐designed sulfuryl fluoride additive for high‐voltage Li metal batteries.