High‐Capacity Electrode Coupling Empowered by a Zwitterionic Hydrogel Electrolyte for Wide‐Temperature, High‐Energy‐Density Aqueous Sodium‐Ion Hybrid Capacitors

ABSTRACT Aqueous sodium‐ion hybrid capacitors (ASIHCs) represent a promising sodium‐based energy storage technology owing to their cost‐effectiveness and high‐power characteristics, yet they face practical implementation barriers from performance degradation at subzero temperatures and energy density limitations imposed by capacitive electrodes. Herein we demonstrate a zwitterionic polymer containing paired cationic/anionic groups (─N + (CH 3 ) 2 /─SO 3 – ) that simultaneously regulates hydrogen‐bond networks and establishes rapid Na + transport channels through selective ion interaction. This strategy yields a zwitterionic hydrogel electrolyte (PASGE) exhibiting a low freezing point (−36°C), exceptional ionic conductivity (58.6 and 12.4 mS cm – 1 at 25 and −20°C, respectively), superior water retention, widened electrochemical stability window (ESW), and mechanical robustness. We further assemble a new ASIHC configuration by pairing a pseudocapacitive δ‐MnO 2 cathode with a pre‐sodiated carbon‐coated NaTi 2 (PO 4 ) 3 anode (δ‐MnO 2 ||PASGE|| pre‐sodiated NTP/C, labeled as MNHC). Benefiting from the high ionic conductivity and large ESW of PASGE, δ‐MnO 2 maximizes its pseudocapacitive behavior, achieving specific capacity comparable to the NTP/C anode (>100 mAh g −1 at 0.3 A g −1 ). Ultimately, our MNHC demonstrates high operating voltage (2.3 V), excellent foldability across −20 to 65°C, and superior energy densities (>58.0 Wh kg – 1 at both 25 and −20°C), surpassing many ASIHCs and even typical aqueous sodium‐ion batteries.