Tertiary‐Amine Based Network Polymer Electrolyte for Improving the Cyclic Stability of Na Metal Batteries with Large Capacity

Abstract Polymer‐based sodium metal battery (SMB) has a great development prospect due to its low cost, good safety, and high theoretical energy density. However, sodium (Na) metal electrode suffers low cyclic stability due to the naturally‐formed unstable solid electrolyte interface (SEI). Herein, 3D network polymer, poly‐bis(3‐(2‐methylaziridin‐1‐yl) propanoate (PBMP) is synthesized, for mechanically robust gel polymer electrolyte (GPE), in which the tertiary‐amine functional group with low‐valence N prefers to react with Na metal to produce a thin and ion‐conducive SEI, realizing Na + fast and uniform plating/stripping. The assembled Na/GPE/Na 3 V 2 (PO 4 ) 3 full battery shows an ultrahigh capacity retention of 97.8% after 2000 cycles under 2 mA cm −2 , which is the top‐level of GPE‐SMB. This work provides a new strategy to construct advanced SEI by regulating functional groups of network polymer for GPE‐SMBs with high safety.