(684e) Vacnt-Based All Solid-State Flexible Micro-Supercapacitors

Hsia, B., University of California, Berkeley
Marschewski, J., University of California, Berkeley
Wang, S., University of California, Berkeley
In, J. B., University of California, Berkeley
Carraro, C., University of California, Berkeley
Poulikakos, D., ETH Zurich
Grigoropoulos, C. P., University of California, Berkeley
Maboudian, R., University of California, Berkeley

Flexible microscale electronic devices are garnering increased research and industrial attention due to possible applications in small form factor consumer electronics, bendable displays, and wearable devices. For autonomous, wireless operation, flexible energy storage devices must also be fabricated to power device circuits and communications. Maintaining a planar architecture for this microscale energy storage could simplify integration, reduce cost, and minimize the footprint of such devices. In particular, micro-supercapacitors present an attractive energy storage solution due to their high power density and long cycle lifetime relative to batteries. Supercapacitors, which rely on electrostatic charge storage at the electrode/electrolyte interface, rather than electrochemical energy storage in the electrode bulk as in batteries, would likely require less maintenance than similar battery technologies, particularly for frequent loading applications such as wireless data transmission. One fabrication and integration challenge for microscale flexible supercapacitors and batteries is the encapsulation of liquid electrolytes, which present safety and reliability concerns due to possible leakage. A flexible solid-state solution, therefore, would be extremely attractive if it could alleviate these difficulties without sacrificing mechanical flexibility.

We demonstrate a facile and scalable technique for fabrication of flexible micro-supercapacitors using vertically aligned carbon nanotube (VACNT) electrodes and an ionic-liquid based gel (ionogel) electrolyte. VACNTs present good electronic conductivity as well as fast ionic transport due to their alignment and are hence a prime candidate for supercapacitor electrodes. The VACNTs are easily patterned and transferred onto flexible substrates in a single step, via a laser assisted process. In conjunction with a flexible, ion conducting ionogel, planar micro-supercapacitor devices are constructed in an interdigitated electrode architecture. Fabricated devices are tested via a variety of electrochemical characterization techniques including cyclic voltammetry, galvanostatic discharge, and AC impedance spectroscopy. Mechanical fatigue tests demonstrate the good flexibility of the device. This novel combination of electrode and electrolyte materials, fabricated via a facile, scalable process, demonstrates an attractive avenue for integrated all solid-state flexible energy storage.