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, Li 2 CO 3 , and Li x PO y F z ), 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 PF 6 − 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, LiPO 2 F 2 , 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||LiNi 0.5 Mn 1.5 O 4 cell maintains cycling over 1000 cycles, and 4.5 V‐class 4.2 Ah Li||LiNi 0.88 Co 0.07 Mn 0.05 O 2 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.