In-situ polymerization of PANI on hydrogel electrolyte enabling all-in-one supercapacitors mechanically stable at low temperatures.

• A mechanically stable and anti-freezing hydrogel electrolyte is obtained. • The hydrogel electrolyte has extensive intermolecular interactions. • The electrolyte has a higher binding energy between ethylene glycol and water. • An all-in-one supercapacitor with highly integrated structure is fabricated. • The supercapacitor shows good electrochemical performance and mechanical stability. Flexible supercapacitors are becoming increasingly popular in portable and wearable electronics. However, conventional flexible supercapacitors typically exhibit laminated multilayer configurations, inevitably causing the irreversibly interfacial slippage or even delamination under deformations. In this study, an all-in-one supercapacitor with highly integrated structure is constructed through in-situ polymerization of conducting polyaniline on a hydrogel electrolyte. Because the extensive intermolecular interactions between polymer chains and nanoparticles can dissipate energy, the prepared hydrogel electrolyte shows outstanding mechanical properties. At the same time, the introduction of ethylene glycol endows hydrogel electrolyte with a higher binding energy between ethylene glycol and water molecule to break hydrogen bonds between water molecules, thus enabling the hydrogel electrolyte to be anti-freezing. Benefiting from the novel all-in-one structure, the device maintains 100% and 97.5% of its initial capacitance after 6000 charging/discharging cycles at room temperature and −20 ℃ respectively. Besides, the highly integrated structure endows the device with excellent capacitance retentions of 99.2% and 97.5% after 5000 bending and stretching cycles respectively. More importantly, the device still works well under bending, twisting, and stretching states at −20 ℃. This work provides an inspiring pathway to develop flexible all-in-one supercapacitors and broadens the practical application range of energy storage devices in various fields. [ABSTRACT FROM AUTHOR]