A multi-responsive self-healing and air-stable ionogel for a vertically integrated device comprised of flexible supercapacitor and strain sensor

We report on the synthesis of multi-responsive self-healing and air-stable ionogel for fabrication of integrated devices of supercapacitor and strain sensor. The ionogel is based on hydrophilic ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate and poly(acrylic acid), crosslinked by N, N'-bis(acryloyl)cystamine-coated gold nanoparticles (AuNP@BACAs). The self-healing of the synthesized ionogel can be triggered by thermal heating or irradiation of near-infrared (NIR) laser light, via the reformation of hydrogen bonds and Au-thiolate interactions. Optically healing with NIR laser can be activated due to the introduction of AuNP@BACAs and the healing rate is faster than that by thermal heating. Using the synthesized ionogel electrolyte and multi-walled carbon nanotube electrodes, a high-performance flexible supercapacitor is fabricated with an areal capacitance of 20.4 mF cm−2, perfect capacitance recovery after repetitive self-healing cycles, and air stability over 30 days in ambient air conditions without encapsulation. Furthermore, the strain sensor fabricated using the same ionogel exhibits the self-healing performance of recovering the gauge factor of 0.85 regardless of the healing method. With the vertically integrated device consisting of flexible supercapacitor and strain sensor attached onto the skin, body-motions are successfully detected using the energy stored by the supercapacitor. These results suggest the high application potential of our fabricated electronic devices based on the single self-healable ionogel to wearable electronics with durability and longevity.