A New (Trifluoromethane)Sulfonylimide Single-Ion Conductor with PEG Spacer for All-Solid-State Lithium-Based Batteries

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 (<i>T</i> _onset ≈ 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 <i>C</i> rates, demonstrating excellent Coulombic efficiency and retaining specific capacity upon prolonged charge/discharge cycling at a relatively high current rate (<i>C</i>/5) at 70 °C.