Anti‐Polyelectrolyte Effect of Zwitterionic Hydrogel Electrolytes Enabling High‐Voltage Zinc‐Ion Hybrid Capacitors

Abstract To date, the exploration of zwitterionic application is confined to the function of electrolyte's additives to improve the properties of the electrolytes. However, reports on the unique properties of zwitterions, namely the anti‐polyelectrolyte effect (APE), as the regulators of the electrochemical stability windows (ESWs) of the zwitterionic electrolytes are scarce. Herein, a zwitterionic electrolyte system is designed and study the relationship between the APE and the ESWs of the zwitterionic electrolytes. The hydrogen/oxygen evolution in the zwitterionic electrolytes is significantly inhibited under the action of the APE. On this basis, the ESWs of zwitterionic electrolytes can be expanded, ultimately achieving an effective improvement in the energy density of zinc‐ion hybrid capacitors (ZHCs). The sulfonic‐based zwitterionic hydrogel electrolytes prepared based on this strategy achieve a wide ESW of 2.58 V and high ionic conductivity of 29.3 mS cm −1 . Meanwhile, the corresponding ZHCs possess a high working voltage of 2.1 V (1.6 V for the traditional ZHCs), a high capacity of 188.9 mAh g −1 and a high energy density of 110 Wh kg −1 . The way utilizing the APE of zwitterions to expand the ESWs opens up a new avenue to improve the energy density of energy storage devices.