Amide Methylation Empowers Concentrated Hydrogel Electrolytes for Wide‐Temperature Flexible Aqueous Sodium‐Ion Batteries

Highly concentrated gel electrolytes combining polymer confinement with concentrated salt chemistry hold great promise for advanced aqueous sodium‐ion batteries (ASIBs). However, strong hydrogen‐bond self‐association in conventional protic polymers occupies functional sites and impedes effective water confinement, limiting ionic conductivity, electrochemical stability, and environmental adaptability. Herein, we design a concentrated gel electrolyte based on an aprotic poly(N,N‐dimethylacrylamide) (PDMA) matrix, which liberates abundant carbonyl sites to establish a robust and dynamically balanced polymer‐ion‐water network. Mechanistic analyses reveal that these freed C=O groups anchor H 2 O and promote anion‐participated Na + solvation, effectively restraining H 2 O activity and lowering the Na + migration barrier. These effects synergistically expand the electrochemical stability window and enable a high ionic conductivity of 43 mS cm −1 , surpassing those of reported hydrogel electrolytes (<30 mS cm −1 ). The assembled Na 3 (VOPO 4 ) 2 F@rGO//NaTi 2 (PO 4 ) 3 /C full cell achieves a high operating voltage of 2.2 V and an energy density of 61.6 Wh kg −1 (70 °C). The restrained water activity enables stable cycling from −20 to 70 °C, with the full cell retaining an energy density of 49.4 Wh kg −1 at −20 °C (85.6% of the room‐temperature value). Moreover, the elimination of interchain hydrogen bonds relaxes the polymer network, facilitating the design of a flexible pouch cell that withstands repeated bending and retains 89.8% capacity after 100 cycles under a fixed 180° bending. This work demonstrates that aprotic polymer design is an effective strategy for constructing robust solvation networks in versatile aqueous energy storage systems.