Excellent Polymerized Ionic-Liquid-Based Gel Polymer Electrolytes Enabled by Molecular Structure Design and Anion-Derived Interfacial Layer

Polymerized ionic liquid (PIL)-based gel polymer electrolytes (GPEs) are well known as highly safe and stable electrolytes but with low ambient ionic conductivity. Herein, we first designed and synthesized an IL monomer with a long and flexible side chain and then mixed it with LiTFSI and MEMPTFSI to construct a PIL-based GPE (denoted as GM-GPE). The special molecular structure of the monomer greatly improves the ionic transport through the PIL chain, and the introduction of MEMPTFSI plasticizer further improves the ionic conductivity, promoting a TFSI^--anion-derived SEI formation to suppress Li dendrite growth and forming an electrostatic shielding effect of MEMP⁺ cations to promote the uniform deposition of Li⁺. Consequently, the as-prepared GM-GPE exhibits high ambient ionic conductivity (4.3 × 10^-4 S cm^-1, 30 °C), robust electrochemical stability, excellent thermal stability, nonflammability, and superior ability to inhibit Li dendrite growth. The resultant LiFePO₄|GM-GPE|Li cell exhibits a high discharge capacity of 150 mA h g^-1 at 0.2 C along with a good cycling stability and rate capability. This work brings about new guidance for the development of high-quality GPEs with high ionic conductivity, high stability, and safety for long cycling and dendrite-free lithium metal batteries.