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

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_0.9Co_0.05Mn_0.05O₂ (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.