A chemically crosslinked hydrogel electrolyte based all-in-one flexible supercapacitor with superior performance

The supercapacitors with conventional multilayer structure exhibit a large contact resistance and tend to delaminate because of the relative displacement under external force. Herein, the all-in-one flexible supercapacitors are fabricated by integrating chemically crosslinked hydrogel electrolytes with conducting copolymer electrodes. The hydrogel electrolyte is prepared by chemically crosslinking reaction of polyvinyl alcohol (PVA) and polyethylene glycol (PEG) with glutaraldehyde (GA) where the hydroxyl groups (-OH) of PVA and PEG react with aldehyde groups (-CHO) of GA to form acetal or hemiacetal in sulphuric acid solution. The prepared hydrogel electrolyte exhibits better mechanical properties (tensile strength of 36 KPa under strain of 117%) and remarkable ionic conductivity (67.1 mS cm−1) than pure PVA hydrogel. Based on this gel electrolyte, a novel flexible supercapacitor with an all-in-one (electrode-electrolyte-electrode) configuration is designed by in situ polymerization of poly (pyrrole-co-aniline) onto PVA/PEG gel electrolyte to achieve exceptional electrochemical performance. This all-in-one configuration can maintain fast charge-carrier transportation and good structural stability. The resulting device shows a large specific capacitance of 773 mF cm−2 at the current density of 0.2 mA cm−2, excellent energy density (54 μWh cm−2) and power density (100 μW cm−2). Under different bending angles or 1000 bending cycles, the capacitance of the device is maintained at 100% which owing to the all-in-one configuration can overcome the relative displacement and avoid the loss of electroactive materials from gel electrolytes when the device is bent. These findings present potential applications in flexible, wearable and smart energy storage devices.