CNT supercapacitors enable harsh-environment energy storage

August 23, 2011 — Rice University researchers created a solid-state, nanotube-based supercapacitors for energy storage, combining aspects of high-energy batteries and fast-charging capacitors with harsh-environment ruggedness.

SEM images. CNT bundles coated with alumina and aluminum-doped zinc oxide in Rice U’s solid-state supercapacitor for energy storage. Credit: Hauge Lab/Rice University.

The supercapacitor uses a solid nanocoating of oxide dielectric material rather than liquid or gel electrolytes. The solid material better withstands extreme heat and cold while performing discharge/recharge functions.

Nanocapacitors. CNT bundles at the center of Rice’s supercapacitors. The electron microscope images at right show the three-layer construction of one of the supercapacitors, which are about 100nm wide. Credit: Hauge Lab/Rice University.

Rice used 15-20nm bundles of single-walled carbon nanotubes (SWCNT) up to 50┬Ám long. Carbon nanotubes were used to give the electrons high surface area, increasing capacitance. Each bundle of nanotubes is a self-contained super capacitor that is 500 times longer than it is wide. A chip could contain hundreds of thousands of bundles.

Transfer scheme. Bundles of vertically aligned SWCNTs to be transferred intact to a conductive substrate. Metallic layers added via atomic layer deposition create a solid-state supercapacitor that can withstand extreme environments. Credit: Hauge Lab/Rice University.

The array was transferred to a copper electrode with thin layers of gold and titanium for adhesion and electrical stability. The nanotube bundles (the primary electrodes) were doped with sulfuric acid to enhance their conductive properties; then they were covered with thin coats of aluminum oxide (the dielectric layer) and aluminum-doped zinc oxide (the counterelectrode) via atomic layer deposition (ALD). A top electrode of silver paint completed the circuit. It creates a metal/insulator/metal structure. Rice asserts that the project is the first of its kind with such a high-aspect-ratio material and ALD fabrication.

Chemist and team leader Robert Hauge devised the energy storage system with an eye on integration into devices from on-chip nanocircuitry to power plant equipment, flexible displays, electric cars, bio-implants, sensors, and other applications, including medical injections.

Results are published in the journal Carbon. Access the article at

Team members included former Rice graduate students Cary Pint, first author of the paper and now a researcher at Intel, and Nolan Nicholas, now a researcher at Matric. Co-authors of the Carbon paper include graduate student Zhengzong Sun; James Tour, the T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science, and Howard Schmidt, adjunct assistant professor of chemical and biomolecular engineering, all of Rice; Sheng Xu, a former graduate student at Harvard; and Roy Gordon, the Thomas Dudley Cabot Professor of Chemistry at Harvard University, who developed ALD.

The research was supported by T.J. Wainerdi and Quantum Wired, in coordination with the Houston Area Research Council; the Office of Naval Research MURI program; the Wright Patterson Air Force Laboratory and the National Science Foundation.

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