Flexible\nAntifreeze Zn-Ion Hybrid Supercapacitor Based\non Gel Electrolyte with Graphene Electrodes

Abstract

Zn-ion\nenergy storage devices employing hydrogel electrolytes are\nconsidered as promising candidates for flexible and wearable electronics\napplications. This is because of their safe nature, low cost, and\ngood mechanical characteristics. However, conventional hydrogel electrolytes\nface limitation at subzero temperatures. Herein, we report an antifreezing,\nsafe, and nontoxic gel electrolyte based on the poly­(vinyl alcohol)\n(PVA)/Zn/ethylene glycol system. The optimal gel electrolyte membrane\nexhibits a high ionic conductivity (15.03 mS cm^–1 at room temperature) and promising antifreezing performance (9.05\nmS cm^–1 at −20 °C and 3.53 mS cm^–1 at −40 °C). Moreover, the antifreezing\ngel electrolyte can suppress the growth of Zn dendrites to display\na uniform Zn plating/stripping behavior. Also, a flexible antifreezing\nZn-ion hybrid supercapacitor fabricated with the optimum antifreezing\ngel electrolyte membrane exhibits excellent electrochemical properties.\nThe supercapacitor possesses a high specific capacity of 247.7 F g^–1 at room temperature under a high working voltage\nof 2 V. It also displays an outstanding cyclic stability at room temperature.\nMoreover, the supercapacitor shows an extraordinary electrochemical\nbehavior and cyclic stability over up to 30 000 cycles at −20 °C under a current load of 5 A g^–1, demonstrating its outstanding low-temperature electrochemical performance.\nBesides, the antifreezing supercapacitor device also offers high flexibility\nunder different deformation conditions. Therefore, it is believed\nthat this work provides a simplistic method of realizing the application\nof flexible antifreezing Zn-ion energy storage devices in a subzero-temperature\nenvironment.