AFiber-ReinforcedPoly(ionic liquid) Solid Electrolytewith Low Flammability and High Conductivity for High-Performance Lithium–MetalBatteries

Construction of polymer-based solid electrolytes with both low flammability and high ionic conductivity for lithium-metal batteries is still a great challenge but highly desirable. Herein, we report on a series of fiber-reinforced poly(ionic liquid) solid electrolytes prepared through an <i>in situ</i> copolymerization of ionic liquid monomers (IL) and poly(ethylene glycol) diacrylate (PEGDA) units with different ratios inside a polyacrylonitrile (PAN) fiber membrane. Such PAN/Poly-IL-PEGDA composite electrolytes demonstrate promising low flammability due to the excellent fire-resistant feature of the employed IL units. Moreover, it is remarkable to see that the optimized PAN/Poly-IL-PEGDA-1 electrolyte also exhibits highly dense structure with low thickness (31 μm), high ionic conductivity (0.32 mS cm^–1 at 30 °C), and wide electrochemical window (up to 4.8 V). As a result, both LiFePO₄//Li and NCM//Li full cells with such an electrolyte exhibit both excellent rate capability and cycling stability. This study provides a simple strategy for preparing composite polymer electrolytes with low flammability and high conductivity for high-performance lithium–metal batteries.