A Fully Self-Healable, Temperature Tolerant and Stretchable Supercapacitor for Operating Integrated Self-Healing Strain Sensor

With the rapid advancement in wearable technology, there has been extensive effort on the development of high performance flexible/stretchable energy storage devices. Among various energy storage devices, supercapacitors are considered to be one of the most promising devices as integrated power supply of wearable electronics owing to many advantages of high power density, high cyclic stability and simple structures. Since the wearable devices are frequently exposed to extreme conditions of enviroments and/or physical damage, however, durability issue has evolved to be a serious challenge for their practical applications. Thus, addition of novel functionality such as self-healing from mechanical damage and tolerance over dramatic changes in temperature to stretchable supercapacitors can be a solution for that. Up-to now, most of the reports showed the self-healing of electrolyte only instead of fully self-healing supercapacitors. Even though many temperature tolerant supercapacitors were reported, there is a few supercapacitors with both self-healing and stability over wide temperature ranges which requires a deliberate design of device structure and materials.<br/>In this work, we report on the fabrication of a fully self-healing, temperature tolerant, and stretchable supercapacitor and its application as a powering device for integrated strain sensor. Organohydrogel with a self-healing via the diol-borate bonding as well as the hydrogen bonding, and the stability over wide temperature range via hydrogen bonding between water and ethylene glycol, could be obtained, respectively. As a self-healing encapsulating film as well as a substrate, a polyurethane film based on oxime-carbamate bonding and hydrogen bonding was synthesized. As a self-healing strectchable electrode, CNT/polyaniline spray-coated on Au nanosheets functionalized with a poly(ether-thioureas) triethylene glycol was used.<br/>By sandwiching the self-healing and temperature tolerant electrolytes with self-healing electrodes on both sides, the fully self-healing supercapacitor stable over temperature changes from -20 to 100 °C was completed. Such fabricated supercapacitor showed the fully self-healing efficiency of 83% even after 5 repetitive cycles of bisection and thermal healing at 65 °C for 6 hr. Also, the supercapacitor was mechaically stable over stretching by 40%, with a capacitance rention of 99%. Furthermore, the whole supercapacitor recovered the electrochemical performance even after bisection and self-healing. The capacitance of the supercapacitor at room temperature was retained over 85% with the temperature changes between -20 and 100 °C. After attachement of the vertically integrated device of the supercapacitor and the strain sensor, bio-signals such as finger-bending and wrist bending could be detected by using the supercapacitor as a self-healing energy storage device. This work suggests that our fabricated fully self-healing, temperature-tolerant, and stretchable supercapacitor should be widely applied to future wearable electronics with a longevity.