The choice of ionic-liquid-like monomers (ILM) for single-ion conducting polyelectrolytes (SICPs) is crucial for the performance of all-solid-state lithium batteries. In the current study, we propose a novel approach for development of SICPs via design and synthesis of a new ILM with long poly(ethylene oxide) spacer between methacrylic group and (trifluoromethane)sulfonylimide anion. Its homopolymer shows an ionic conductivity that is ∼5 orders of magnitude higher (9.2 × 10-8 S cm-1 at 25 °C), in comparison with previously reported analogues, while the conductivity of its random copolymer with poly(ethylene glycol)methyl ethermethacrylate reaches the levels of 10-6 and 10-5 S cm-1 at 25 and 70 °C, respectively. The copolymer provides excellent thermal (Tonset ≈ 200 °C) and electrochemical (4.5 V vs Li+/Li) stabilities, good compatibility with Li metal, and effective suppression of dendrite growth. Li/SICP/LiFePO4 cells are capable of reversibly operating at different C rates, demonstrating excellent Coulombic efficiency and retaining specific capacity upon prolonged charge/discharge cycling at a relatively high current rate (C/5) at 70 °C. © 2024 Elsevier B.V., All rights reserved.