Modulating LithiumMetal Interphase Structures viaFunctional Design of Polymeric Ionic Liquids for Quasi-Solid-StateBatteries

Despite the great potential of Li-metal anodes, the high reactivity of Li metal and dendritic Li growth hinder the stable operation of Li-metal batteries. Artificial Li protective layers have been introduced as a solution to stabilize the interface between the electrolyte and the Li-metal anode. In this study, we propose a functionally designed polymeric ionic liquid (PIL) for the interfacial stabilization of Li-metal anodes in quasi-solid-state batteries. Polycationic PILs are designed to form conductive and robust interphases at the PIL/Li while serving as an effective electrostatic shield to suppress dendrite growth. In addition to the optimized composition for facile Li⁺ transport kinetics in the PIL, the anion configurations in the PIL are engineered to produce highly ionic-conductive Li₃N and to increase the concentration of LiF in the solid–electrolyte interphase. A PIL-coated Li-metal electrode (PIL thickness ∼5 μm) exhibits reduced interfacial resistance and enhanced cycling performances for the Li symmetric cell and full cell with a quasi-solid-state electrolyte and a high-loading LiNi_0.8Co_0.1Mn_0.1O₂ cathode (4 mAh cm^–2). These findings provide insights into the design of protective PIL layers for constructing a stable interface between the electrolyte and the Li-metal anode.