Ionic‐Ligand‐Assisted Transport in Fluorinated Poly(ionic liquid) Electrolytes Enables 515 Wh Kg −1 Solid‐State Lithium Metal Batteries

ABSTRACT Decoupling ionic conductivity from polymer segmental relaxation while maintaining interfacial stability remains a pivotal challenge for solid polymer electrolytes (SPEs). In this study, we construct an ionic‐ligand‐assisted transport framework by copolymerizing a fluorinated acrylate polymer with a poly(ionic liquid) (PIL) and optimizing the lithium bis(fluorosulfonyl)imide (LiFSI) salt concentration. Density functional theory and molecular dynamics simulations reveal that cationic PIL moieties strongly anchor FSI − anions, creating anion‐rich, spatially correlated coordination pathways that facilitate efficient Li + hopping. The optimized electrolyte exhibits a high ionic conductivity (0.38 mS cm −1 ) and an exceptional Li + transference number (0.77) at 30°C. The fluorinated backbone and PIL synergistically expand the oxidative stability window to 4.94 V and promote an inorganic‐rich solid electrolyte interphase (SEI) on the Li‐metal anode. Consequently, Li||Cu cells cycle stably for over 400 cycles with 99.1% average Coulombic efficiency. Solid‐state Li||LiNi 0.9 Co 0.05 Mn 0.05 O 2 (NCM90) cells retain ≈81.0% capacity after 600 cycles at 4.3 V, and ≈83.1% capacity after 200 cycles at 4.5 V. Moreover, a high‐energy‐density (515 Wh kg −1 ) solid‐state pouch cell with an ultrathin Li anode (50 µm) and a high‐loading NCM90 cathode (≈56 mg cm −2 ) delivers stable cycling and exceptional safety. This ionic‐ligand regulation paradigm provides critical mechanistic insights for designing high‐performance and high‐safety solid‐state batteries.