All-temperature flexible supercapacitors enabled by anti-freezing and thermal-stable hydrogel electrolyte.

All-temperature flexible supercapacitors have not been realized because of challenges from conventional hydrogel electrolytes. Massive water in hydrogel electrolytes inevitably freeze and restrict ion transport at subzero temperatures, and their structures are unstable under high temperature. Here, all-temperature flexible supercapacitors are reported based on anti-freezing and thermal-stable montmorillonite/polyvinyl alcohol (MMT/PVA) hydrogel electrolyte. MMT materials enhance thermal stability of hydrogel, and their lamellar structures facilitate ion conduction due to formation of oriental conductive pathways. The aqueous electrolyte with freezing point below -50 oC is employed by simply introducing dimethyl sulfoxide. The electrolyte exhibits high ionic conductivity of 0.17×10-4 and 0.76×10-4 S cm-1 under -50 and 90 oC, respectively. The supercapacitor delivers high capacities under wide temperature range from -50 to 90 oC, and display excellent cycling stability over 10000 cycles. Because of superior mechanical properties of the hydrogel electrolyte, the device gives stable energy capacity under flexible conditions.