In situ polymerized flame-retardant EGMEA-based gel electrolyte for stable and safe sodium metal batteries.

An in situ polymerized EGMEA-based gel electrolyte confining liquid while preserving solvation imparts flame retardancy, a 0.69 Na+ transference number, and a 4.63 V electrochemical window, enabling dendrite-free Na‖Na cycling and Na‖Na3V2(PO4)3 cells with 98.4% (150 cycles) and 84.6% (600 cycles at 60 °C) capacity retention.