All-Temperature Flexible Supercapacitors Enabled by\nAntifreezing and Thermally Stable Hydrogel Electrolyte

Abstract

All-temperature flexible\nsupercapacitors have not been realized\nbecause of challenges from conventional hydrogel electrolytes. Large\namounts of water in hydrogel electrolytes inevitably freeze and restrict\nion transport at subzero temperatures, and their structures are unstable\nunder high temperature. Here, all-temperature flexible supercapacitors\nare reported based on an antifreezing and thermally stable montmorillonite/poly­(vinyl\nalcohol) (MMT/PVA) hydrogel electrolyte. MMT materials enhance the\nthermal stability of the hydrogel, and their lamellar structures facilitate\nion conduction due to formation of oriented conductive pathways. The\naqueous electrolyte with a freezing point below −50 °C\nis employed by simply introducing dimethyl sulfoxide. The electrolyte\nexhibits high ionic conductivity of 0.17 × 10^–4 and 0.76 × 10^–4 S cm^–1 under\n−50 and 90 °C, respectively. The supercapacitor delivers\nhigh capacities under a wide temperature range from −50 to\n90 °C and displays excellent cycling stability over 10000 cycles.\nBecause of the hydrogel electrolyte’s superior mechanical properties,\nthe device gives stable energy capacity under flexible conditions.