Alt-BEAM Archive
Message #05202
To: beam@sgiblab.sgi.com
From: "John A. deVries II" zozzles@lanl.gov
Date: Fri, 09 Jul 1999 09:59:18 -0600
Subject: [alt-beam] Ultracapacitors
From the July 1999 "Reflections", a monthly publication of the Los Alamos
National Laboratory
Serendipitous discovery: From unexpected impurity to vital additive (by
Todd Hanson)
Over the past few years, the starting materials, or monomers, provided by
John Ferrari's team at the University of Texas in Dallas for making
conducting polymer active materials for ultracapacitors have been of the
highest quality. The team's expertise in organic chemistry provided the
foundation for the development of the ultracapacitor, yet it was an
impurity in one batch of monomers that led to a breakthrough in
ultracapacitor research.
Last summer, Steven Shi of Electronic and Electrochemical Materials and
Devices (MST-11) was fabricating an ultracapacitor using conducting polymer
as the electrode active material. The polymer was electropolymerized from
its monomer solution onto a carbon paper disk bonded to a current collector.
Shi had used up one batch of the monomer and was starting with a fresh
batch -- subsequently named the "April batch" - when the disk displayed a
rusty red color rather than the usual black. Instead of discarding the
material and starting over, Shi decided to investigate.
He found that the rust-colored disk was significantly superior to the
original black in terms of polymer morphology and material stability. The
red material had a highly porous, open structure, with polymer grain size
in the sub-micron range, while the black material showed a relatively
compact structure with a polymer grain size in he range of several microns.
The new morphology provided a large, effective, electrolyte-accessible
polymer surface area, leading to fast charge/discharge dynamics. More
surprisingly, the red material also helped extend the device cycle life in
pulsed discharge mode from 100,000 cycles to 2.7 million cycles.
Shi brought this discovery to the attention of principal investigator
Shimson Gottesfel, also of MST-11, who suggested that Shi test subsequent
batches. Using new batches of the monomer, the electrodeposited polymer
returned to its ordinary black color, and the cycle life of the
ultracapacitor dropped back to 100,000 cycles. It was clear that the April
batch was an anomaly.
Gottesfeld suggested that Ferraris re-analyze the April batch, and the
Texas team confirmed that it contained a previously undiscovered component.
The impurity had been hidden during the initial analysis beneath a large
spike in the gas chromatography spectrum -- an analytical method used to
determine the chemical components of complex mixtures. It was easy to miss.
Using information gained from the analysis, Shi added the component to a
solution of the pure monomer and electropolymerized the active material
from that mixed solution. The resulting polymer showed the same superior
properties as the April batch. Somehow, the impurity had improved the
quality of the conducting polymer. The unexpected component has since been
promoted from an impurity to a vital additive.
Uncertain as to exactly what makes the new conduction polymer more robust
-- either the second component strengthens the conducting polymer's bonding
to the carbon or provides cross-linking in the polymer -- the Los Alamos
researchers continue to investigate, aiming at further improvements in
ultracapacitor technology.
(copyright 1999 DOE/UC, yaddita, yaddita, yaddita)
p.s. hey - YOU try typing "electropolymerized" a few times and see what
happens to YOUR fingers!
---------------------------------------------------------------
John A. deVries II
zozzles@lanl.gov
------------------------------------------------------------------------
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