Flame-retardant gel polymer electrolyte and interface for quasi-solid-state sodium ion batteries

Polymer electrolyte is favored in battery research because of its good flexibility, light weight and preferable interfacial contact. However, the development of which is hindered by the low ionic conductivity at room temperature. Herein, a flexible PPEGMA-based gel polymer electrolyte (PGT32-5%) was prepared via in-situ thermal cured technique, plasticized by nonflammable triethyl phosphate and supported by glass fiber. The optimized flame-retardant electrolyte, PGT32-5%, exhibits a high ionic conductivity (0.91 mS cm⁻¹ at 27 °C and a wide electrochemical window (4.8 V). And an artificial interface between polymer and Na metal anode was built to guarantee the superior cycling stability (capacity retention of 91% after 400 cycles) of quasi-solid-state Na₃V₂(PO₄)₃|PGT32-5%|Na battery. Further, the interfacial property and effect on discharge behavior were analyzed in depth, which paves the way for designing polymer electrolytes with superior comprehensive performances in future.