MXene/Zwitterionic Hydrogel Oriented Anti‐freezing and High‐Performance Zinc–Ion Hybrid Supercapacitor.

With the wide application of portable electronic devices, zinc–ion hybrid supercapacitors (ZIHCs) have aroused great interest. However, balancing the low‐temperature performance and high energy density of ZIHCs remains a huge challenge. Herein, a zwitterionic hydrogel electrolyte (ZHE) loaded with carboxymethylcellulose and MXene is designed for ZIHCs, which shows excellent frost resistance and high output voltage. Carboxymethylcellulose and MXene enhance the flexibility and conductivity of the zwitterionic hydrogel electrolyte. Moreover, When ZnCl2 is introduced into a gel electrolyte, it induces an increase in the rate of ion transport, which enables a broadening of the operating temperature of the hydrogel (−40 °C–25 °C). As a result, Zn//AC ZIHCs based on ZHE show a high voltage window of 2 V, a high energy density (specific capacity) of 137 Wh kg−1 (247 F g−1), and the potential for wearable devices. This study will provide an effective strategy for the design of hydrogel ZIHCs with wide voltage windows, high energy density, and high practicality. [ABSTRACT FROM AUTHOR]