Self‐Sacrificing Flame‐Retardant Oligomer Enables Anion‐Dominated Solvation Structure for High‐Safety and Long‐Life High‐Voltage Lithium‐Metal Batteries

ABSTRACT The commercialization of NCM811‐lithium metal batteries has long been constrained by two major bottlenecks: electrolytes’ flammability and poor electrode interface compatibility. This study designed a multifunctional unsaturated oligomer electrolyte additive (PE) as a coordinator and martyr for batteries’ safety and stability. It integrates flexible segments to promote lithium‐ion transport, phosphorus‐containing segments to achieve both vapor‐phase and condensed‐phase flame retardancy, and the synergy of P═O and C═C effectively stabilizes both the lithium‐metal anode and high‐voltage cathode. This additive selectively partitions into Li + solvation shell, where P═O bond coordinates with Li + and C═C bond establishes anion‐C═C interaction with PF 6 − , constructing a unique anion‐dominated solvation environment in commercial electrolyte with conventional lithium salt concentration to trigger highly stable and LiF/Li x PO y ‐rich interfacial layer formation on electrode surface. At low addition levels, electrolyte flammability is significantly reduced while battery performance is comprehensively enhanced. NCM811‖Li batteries achieved stable cycling for over 500 cycles at 1 C, maintaining 80% capacity retention. Even at 5 C, they retained 76% capacity after 160 cycles. By strategically designing localized molecular structures to synergistically enhance flame retardancy, ion transport, and interfacial stability within a single molecule, this study provides a promising paradigm for the development of electrolytes for high‐safety, long‐life, and high‐energy‐density lithium batteries.