In this work, we report a novel UV-crosslinked polymer-in-concentrated ionic liquid system (PCIL) based on PEO, lithium bis(fluorosulfonyl)imide (LiFSI) and N-propyl-Nmethylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) ionic liquid (Li + :IL molar ratio = 1:1). By focusing on the enhancement of ion transport, electrochemical stability, and cell performance, we seek to tackle a critical gap in the current understanding of PEO-based SPEs. The obtained PCIL-SPEs achieved high ambient temperature ionic conductivity, wide electrochemical stability window, stable and reversible cycling toward Li metal electrodes and promising solid-state LMB performance. Thus, by incorporating concentrated ionic liquids with UV-crosslinking to form a robust SPE, we shed light on the potential of PEO-based SPEs to meet the rigorous demands of high-performing solid-state LMBs and pave the way for their practical application in future advanced energy storage systems.