The pursuit of advanced energy storage technologies has significantly featured the role of lithium metal batteries (LMBs) owing to their superior energy density and potential for enabling long-range electric vehicles. However, the widespread adoption of LMBs is hindered by safety concerns related to liquid electrolytes, which are prone to flammability and stability issues. This has promoted the exploration of solid electrolytes as a safer alternative. The pioneering work of Wright and Armand in 1970s ignited the interest and passion for research into solid polymer electrolytes (SPEs) for rechargeable solid-state batteries. Since then, polyethylene oxide (PEO) has become a frontrunner in SPEs due to its high safety, ease of processing, low cost, and good compatibility with lithium metal, making it attractive for integration into next-generation LMBs. High molecular weight PEO offers the benefits of preventing Li dendrite formation due to its superior mechanical properties and enhancing cycling stability compared to its lower molecular weight counterpart. However, ionic conductivity of PEO at room temperature is inadequate (up to 10 -6 S cm -1 ) because its semicrystalline structure which hinders chain mobility, essential for ion transport, often requiring higher temperatures for effective application. Additionally, PEO-based solid polymer electrolytes (SPEs) are limited by a narrow electrochemical stability window (ESW < 4V vs. Li + /Li) due to the low oxidative stability of ether oxygen. These drawbacks considerably constrain their practical use in high voltage solid-state lithium metal batteries (LMBs). To overcome these issues, research has focused on modifying the PEO microstructure, including the addition of inorganic fillers, plasticizing ionic liquids, 10 copolymerization, and creating crosslinked PEO matrices. Ionic liquid (IL)-based electrolytes have gained significant interest in recent years due to their superior properties, such as low vapor pressure, nonflammability, and outstanding thermal and chemical stability. Shin et al. investigated the impact of C3mpyrTFSI ionic liquid on the ionic conductivity of PEO-based ternary polymer electrolytes, and demonstrated that the inclusion of highly conductive room temperature ILs significantly enhances ionic conductivity, surpassing the limits previous observed in IL-free electrolytes. Crosslinking, as a versatile polymerization technique, is often used to improve the mechanical property and hinder polymer crystallization of plasticized SPEs. Watanabe et al. first studied the crosslinked PEO-LiClO4 systems which showed decreased PEO crystallinity by decreasing Tg from -22 to -30°C and enhanced ionic conductivity from 10 -9 to 10 -5 S cm -1 at 30°C compared to linear PEO system (EO/Li mole ratio = 20). Joost et al. further explored ionic mobility in crosslinked PEO-based ternary SPE systems that incorporate C4mpyrTFSI ionic liquid with relatively low concentration of LiTFSI (25 mol%), demonstrating a decrease of Li + -EO interactions in the ternary system due to the additional TFSI -anions from ionic liquid that contributes to the high ionic conductivity. The crosslinking process, induced by UV irradiation, helps to form a stable network that enhances the mechanical integrity of the SPE while accommodating the beneficial properties of ILs. The effectiveness of UV-induced crosslinking in the development of polymer-plasticiser-salt ternary systems was further validated by other researchers. In recent years, inspired by the concept of high concentrated electrolyte in traditional liquid electrolytes, there is growing interest in concentrated ionic liquid (CIL) electrolytes due to their advantageous properties such as expanded electrochemical stability window, 21 high transference number, high rate capability, and enhanced cycling stability. Recent work from Pal et al. identified the use of ether-aided concentrated LiFSI-C3mpyrFSI ionic liquid electrolyte as an effective approach to enhance ion transport, interfacial stability, and support fast charging. These desirable properties make them promising candidates to work with the crosslinking strategy for developing high-performance PEO-based SPEs. Thus, one promising approach to form a robust PEO-based SPE is to combine crosslinking with the incorporation of CILs, which shows great potential in further suppressing PEO crystallinity, improving ionic conductivity, expanding electrochemical stability while maintaining safety and mechanical integrity.