A hydrogel electrolyte with dynamically Tunable mechanical properties for wide-temperature flexible supercapacitor

The application of conductive polymer hydrogels in flexible energy storage devices has gained a great deal of attention. In this paper, the hydrogel integrating water retention and antifreeze properties is realized by the organic binding of polyvinyl alcohol (PVA) chains and NaClO₄. The composite hydrogel is assembled with MnO₂/carbon fiber and activated carbon fiber to constitute a flexible quasi-solid-state supercapacitor. The capacitor can cycle 25,000 times with the capacitance retention of 81 % when exposed directly to the external environment. In addition, the capacitor can store charge consistently and stably between −40 °C and 40 °C. This demonstrates the excellent environmental stability of the composite gel, which ensures stable operation of the device under extreme conditions. Excitingly, the mechanics of PVA composite gel electrolyte can be dynamically coordinated using the Hofmeister effect. The longer the flexible quasi-solid supercapacitor is soaked in 1.5 M Na₂SO₄ solution, the stronger the mechanical properties are. There are new thoughts in engineering new flexible supercapacitors with this biological compatibility and multi-functional conductive hydrogel.