In Situ Polymerized “Solvated-Ionic-Liquid in Oligomer” Composite Electrolyte with Multiscale Anion Immobilization for Solid-State Lithium-Metal Batteries

In situ polymerized solid-state electrolytes for lithium-metal batteries suffer from the inherent conflict between robust polymer network and delicate Li⁺ transportation coordination structure. Here, we demonstrate a multiscale engineering strategy through the in situ construction of a solid-state "Solvated-Ionic-Liquid in Oligomer" electrolyte to address this trade-off. Critically, the poly(vinyl carbonate) (PVC) oligomer network is designed to preserve 86.8% of the [Li(Tetraglyme)]⁺ solvation structure of solvated ionic liquid (SIL), which enables high conductivity and a wide electrochemical window. This oligomer framework functions as a molecular-scale anion trap, collaboratively working with a nanoscale fluoroethylene carbonate (FEC)-derived LiF-rich solid electrolyte interphase and a macroscale alumina fiber scaffold for improving Li⁺ transportation and mechanical robustness. This triple-component synergy unlocks a high Li⁺ transference number (0.465) and a remarkable ionic conductivity (4.32 mS cm⁻¹), enabling a stable lithium-metal interface (700 h in Li/Li symmetric cells) and exceptional cycling durability in Li/LiFePO₄ batteries (79.7% capacity retention after 1000 cycles at 3 C).