Degradable Polymer Electrolytes Encapsulated with Ionic Liquids for Enhanced Ionic Conductivity and Stable Interfaces in Lithium-Metal Batteries

In green and sustainable energy utilization, solid electrolytes are called to be environmentally friendly and degradable. Meanwhile, there has been a concerted effort to improve ion transport and interfacial stability of solid-state electrolytes to enhance solid-state battery (SSLBs) development. Herein, we have made a polymer electrolyte encapsulated with a degradable ester-based ionic liquid (IL) of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄TFSI). This enables rapid degradation to be achieved, up to complete degradation within 12 h under alkaline conditions, owing to the robust interplay occurring between the Pyr14⁺ cations present in the IL and the ether functional groups; this interaction fosters a consistent encapsulation of the IL within the polymeric matrix structure, thereby introducing a large number of Li⁺. At 25 °C, an ionic conductivity of 7.6 × 10^-4 S cm^-1 is achieved. In addition, Pyr₁₄TFSI facilitates the in situ development of a solid electrolyte interphase (SEI) layer abundant in lithium fluoride (LiF) and lithium nitride (Li₃N), which effectively suppresses lithium dendrite growth, representing stable cycling performance even at 25 °C. Therefore, this work provides a simple and feasible approach for designing green SSLBs with degradability, fast ion conduction, and good interface stability.