Stretchable electronics have received increasing attention due to their broad applications in the emerging wearable devices, biomedical devices, epidermal electronics and biointegrated electronics that must sustain large deformations and conform to surfaces with complicated geometries while maintaining their normal functions and reliability. Examples include interconnects, loudspeakers, pressure and strain sensors, temperature sensors, light emitting diodes (LEDs), radio frequency (RF) devices, field effect transistors, epidermal electronics, and integrated circuits. To integrate these stretchable electronics into a power-independent stretchable system in an elegant way, stretchable energy conversion/storage devices become of paramount importance. We report a new type of highly stretchable and reliable supercapacitor based on crumpled vertically aligned carbon nanotube (CNT) forests transferred to an elastomer substrate. The stretchable SCs consist of two crumpled CNT forest electrodes and one solid-state electrolyte layer of PVA-KCl, which also serves as a separator for the SC. The CNT forests are first transferred onto the prestrained elastomer substrate with the assistance of a thermal annealing process. Then, a thin layer of PVA-KCl gel is cast onto the CNT forest electrodes as the electrolyte and separator. After that, the two stretchable electrodes from crumpled CNT-forests covered with the gel electrolyte are assembled together to form a stretchable SC device. The crumpled CNT-forest electrodes have two major advantages: (1) CNT forests are very stable and can be easily patterned by annealing-assisted contact transfer, and (2) the vertical CNT forests have a larger surface area compared to a conventional thin flat film, and can be easily modified to be hybrid SCs, particularly in the crumpled states. Additionally, the three-dimensionally interconnected CNT forest on the top layer maintains the electrical conductivity under stretching deformations even larger than the prestrains defined in the fabrication. This simple method makes it possible to fabricate mechanically reliable, robust, wavy stretchable electrodes with improved performance. Electrochemical measurements demonstrate that the resultant stretchable crumpled CNT forest electrodes and SCs possess good energy and power densities, comparable with previous CNT-based supercapacitors in literature, and the electrochemical performance of the stretchable SCs show little variation even under applied tensile strains of 300%. either the uniaxial or biaxially stretchable SCs with crumpled CNT-forest electrodes showed similar specific areal capacitance compared to the sate-of-the-art CNT supercapacitors. Moreover, the crumpled CNT-forest supercapacitors exhibit large area strain (800% for biaxially, and 300% for uniaxially crumpled CNT supercapacitors) while maintaining high specific capacitance. The approach developed in this work offers an alternative strategy for developing novel stretchable energy devices with vertically aligned nanotubes or nanowires for advanced applications in stretchable, flexible and wearable electronic systems.


Highly Stretchable Supercapacitors via Crumpled Vertically Aligned Carbon Nanotube Forests

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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