South Korean capacitors for next generation of hybrids/EVs
- Super Charged
A tiny South Korean company is out to make capacitors powerful enough to
propel the next generation of hybrid-electric cars
By Glenn Zorpette
Let's say it's 2010, and you're boiling off midlife ennui or burnishing your
golden years in time-honored fashion: by zooming around in a
high-performance road machine. The car accelerates powerfully, and yet it
moves quietly and nimbly, slaloming through curves like a go-cart. Best of
all, it sips gas like a connoisseur enjoying 40-year-old Armagnac. Would you
believe you owe these rejuvenating, guilt-free thrills to a bunch of
Not just any capacitors, of course. To understand what's going on under the
hood of this car, you'll need to leave behind the Lilliputian world of the
picofarad and the microfarad and enter the realm of the kilofarad. It is a
place where NessCap Co., in Yongin, South Korea, holds sway.
750-8, Gomae-Ri, Kiheung-Eup, Yongin,
Kyonggi-Do, 449-901, Republic of Korea
Tel 82-31-289-0721~5 Fax 82-31-286-6767~8
NessCap is one of about 10 makers of ultracapacitors, devices that can store
so much charge that they are beginning to blur the functional distinction
between the capacitor and the battery. And according to some experts, nobody
does it better than NessCap, which offers a unit rated at an impressive 5000
farads at 2.7 volts in a package a little bigger than a half-liter soda
bottle. NessCap's capacitors "perform as well as or better than any others
we've ever tested, in terms of energy and power density," says Marshall
Miller, a research engineer at the University of California at Davis, where
he specializes in testing advanced capacitors and other devices.
Research Engineer, ITS-Davis
University of California, Davis
One Shields Avenue
Davis, California 95616-8762
Ultracapacitors made by NessCap and others are just now starting to show up
in products ranging from toys to experimental buses, basically as
alternatives to batteries. The worldwide market isn't large; it was just US
$38 million in 2002, the most recent year for which figures are available,
according to the research firm Frost & Sullivan, in San Antonio. But NessCap
and the handful of other makers of the largest ultracapacitors all have
their sights set on the automotive market, which could do for their business
what the iPod did for sales of MP3 songs. Frost & Sullivan, at least, is a
believer; the company optimistically predicts total 2007 revenues for
ultracapacitors of $355 million.
Frost & Sullivan
7550 W Ih 10
San Antonio, TX 78229
North America Team Leader
210-247-2403 Fax: 210-348-1003
Environment, Aerospace & Defense, Transportation, and Chemicals
210-247-2440 Fax: 210-348-1003
210-247-2450 Fax: 210-348-1003
Asia Pacific, Australasia & China
Tel: +603 6204 5832
On paper, anyway, the idea is not far-fetched. In comparison with batteries,
ultracapacitors can put out much more power for a given weight, can be
charged in seconds rather than hours, and can function at more extreme
temperatures. They're also more efficient, and they last much longer-in
tests at the Idaho National Engineering and Environmental Laboratory, in
Idaho Falls, upwards of 500 000 charge-discharge cycles have been recorded.
Automotive traction batteries, for comparison, have much shorter lifetimes,
particularly if they are discharged deeply.
Pondering the relative strengths of capacitors and batteries, Joel
Schindall, associate director of the Laboratory for Electromagnetic and
Electronic Systems at the Massachusetts Institute of Technology, in
Cambridge, says: "In all ways other than energy density, an electric field
is superior to chemistry for storing energy regeneratively, because it is
completely reversible" and therefore intrinsically efficient and durable.
Part of Schindall's research focuses on advanced materials that could be
used as electrodes in future ultracapacitors.
Professor Of The Practice and LEES Associate Director
(617) 253-3934 Office: 10-097
Double Layer Capacitors: Automotive Applications and Modeling
Ultracapacitors are now establishing themselves in niches demanding a power
source that can recharge quickly, be sealed into a system that has to last
for years, or put out prodigious amounts of power in short bursts.
Tokyo-based Ricoh Co. is using them in copier machines to store the energy
needed to warm up the machines quickly, minimizing time spent in the
energy-wasting standby mode. Makers of high-end car stereo amplifiers are
using ultracapacitors to deliver the surges of power demanded by musical
crescendos, without straining the vehicle's battery.
Another use is in solar tiles; a new twist in landscape architecture,
they're used to guide pedestrians at night, by storing solar-generated
electricity during the day and using it to power a small light-emitting
diode panel after dark [see photo, "Bright Idea"]. Sealed into a walkway,
wall, or staircase, these clear, rugged tiles have to last for a decade or
more, working without fail night after night, withstanding subfreezing and
sweltering temperatures alike-criteria only ultracapacitors can fulfill.
And then there are cars. The hybrid-electric vehicle, in its various forms,
is poised for an increasing share of the automotive market in several parts
of the world, including the United States. And ultracapacitors have already
found their way into hybrids, albeit in a minor role: hardly noticed among
the Toyota Prius's many celebrated technical breakthroughs is the fact that
it uses ultracapacitors, from Panasonic, to power an electric-hydraulic pump
in the mechanical braking system.
It's just the start of what some experts say ultra-capacitors will do for
hybrids. For example, with their lightning-fast charge and discharge
capability, ultracapacitors could handle the power surges needed for
accelerating, allowing engineers to use a smaller battery pack in the
vehicle (and eventually, perhaps, no battery pack at all). Shielded from
high-current pulses, the batteries would last longer, too.
There are other intriguing possibilities, such as using the devices to give
more or less ordinary cars "stop-and-go" operation, in which the gasoline
engine is extinguished at stops and started instantly when the brake pedal
is released. Ultracapacitors and a powerful starter motor would instantly
jolt the engine back to life. Such vehicles would also make use of
regenerative braking, converting into electricity the kinetic energy
otherwise thrown off as heat in the brakes and storing that electricity in
SO WHAT WILL IT TAKE FOR ULTRACAPACITORS to find a home under the hood?
First, they've got to be a lot cheaper. Today, at roughly $9500 per
kilowatthour, ultracapacitors are too expensive by a factor of five, at
least, for cost-conscious carmakers. Second, automotive engineers would like
to see the devices store more energy (as opposed to power) per unit weight,
which would let the devices take over more of the energy-storage burden from
batteries in future vehicles.
If NessCap and its competitors can achieve those goals and crack this
market, the long-term future looks good. No one knows when, or even if, the
fuel-cell car will become a mass-market reality-the estimates range from 10
to 30 years. But if it does happen, it's likely that ultracapacitors will be
a big part of the reason. Fuel cells, by themselves, deliver power too
sluggishly to briskly accelerate a full-size car. They must be mated to a
faster-acting energy-storage device, and for this coupling, ultracapacitors
are superior in many respects to batteries.
"Capacitors and fuel cells are made for each other," insists Andrew Burke, a
specialist on ultracapacitors and a research engineer at the University of
California, Davis. Honda, for example, used only ultracapacitors to
supplement the fuel cell in its experimental FCX-V3 and FCX-V4 vehicles,
several of which have been leased in California and Japan [see illustration,
"Fueling Around"]. For these vehicles, Honda used its own ultracapacitors.
Andrew F. Burke
Research Engineer, ITS-Davis
At first glance, at least, NessCap may seem an unlikely candidate to get
ultracapacitors into a production car. NessCap's three main
competitors-Maxwell Technologies in San Diego; Epcos in Munich, Germany; and
Panasonic in Osaka, Japan-all have either deep-pocketed parent companies or
revenue from other product lines with which to support their ultracapacitor
development. (Panasonic ultracapacitors are manufactured by Matsushita
Electronic Components Co., in Kadoma City, Japan.)
But what NessCap lacks in resources, it makes up in resourcefulness and
determination. The company was founded in 2001 by Sun-wook Kim, a Korean
entrepreneur and former research director at the Daewoo Group. Although Kim
has a few other ventures, including a new organic-LED display factory in
Singapore, NessCap is basically a stand-alone enterprise that will either
succeed or fail on the strength of its ultracapacitors and on its
executives' ingenuity in promoting them.
Certainly, the company is efficient: all of NessCap's 65 employees work in a
boxy, yellowish, blue-trimmed building in a gritty suburb outside the Korean
industrial city of Suwon. It houses NessCap's factory, offices, and R&D
laboratories and its quality-control, testing, and shipping and receiving
departments, as well as a subsidiary consumer-electronics spinoff and a
warehouse. And though it's a small company, NessCap makes all its own
electrodes for its capacitors. Among the company's closest competitors, only
Panasonic can also make that claim, says NessCap's chairman, Inho Kim (who
is not related to Sun-wook Kim).
This distinction is important, he says, because he expects electrode
refinements to be the main source of future improvements in ultracapacitor
performance-greater energy storage, for example-and decreases in cost.
Electrode technology, Inho Kim estimates, determines "70 or 80 percent" of
the capacitor's performance. "If you own the electrode-manufacturing
technology, you can basically do anything," he argues.
ULTRACAPACITOR DEVELOPMENT PROJECT
GOAL: Cut the cost of ultracapacitors are superior to batteries in many
respects and will almost certainly be used increasingly in hybrid-electric
and fuel-cell cars
ORGANIZATION: NessCap Co.
CENTER OF ACTIVITY: NessCap's facility in Yongin, South Korea
NUMBER OF PEOPLE ON THE PROJECT: About 15
BUDGET: Approximately US $2 million
TO GET AN IDEA of where these improvements will come from, you've got to
understand what separates an ultracapacitor from an ordinary capacitor
(other than a whole lot of farads). First, consider the classic
parallel-plate capacitor, a sandwich of two conductive plates separated by
an insulator, or dialectric. When the plates are connected to the positive
and negative terminals of a battery, opposite charges separate from each
other and accumulate on the plates. Driven by the battery's voltage, an
electric field permeates the dielectric. Associated with that field is a
voltage that opposes the battery's voltage.
The field holds the accumulated, opposing charges apart; in doing so, it
stores energy. So, unlike a battery, which stores energy in chemical form, a
capacitor stores energy in an electric field; there are no moving parts and
no chemical changes of state. To use a capacitor's energy, you just let its
accumulated charges flow through a circuit, driven by the voltage associated
with the field.
Capacitance is simply a measure of how much charge a capacitor can store for
a given voltage. In mathematical terms, the capacitance equals the charge on
the plates divided by the voltage difference between them. The charge,
however, is proportional to the area of the plates; larger plates can hold
more charge. And the voltage is related to the distance between the two
plates; less separation allows more charge to accumulate for a given
voltage. So to wring the most capacitance from a device, you want plates, or
electrodes, that have a large area, and you want to separate those plates by
a very small distance.
In the early 1960s, at the once mighty research laboratories of Standard Oil
of Ohio (Sohio), researchers discovered that two pieces of activated carbon
immersed in a liquid electrolyte formed an amazingly good capacitor, owing
mainly to the fact that the activated carbon's myriad microscopic nodules
had enormous surface area. Sohio licensed the technology to NEC Corp.,
Tokyo, in 1971, but it was Panasonic that pushed the concept hardest in the
1980s, followed by various projects sponsored by the U.S. Department of
Energy in the 1990s.
Since Sohio's initial experiments 40 years ago, the basic concept has not
changed much. Coat two metal-foil electrodes with activated carbon and put a
paper separator between them. Immerse the whole thing in a liquid
Attach wires from the terminals of a battery to the two metal foils, and
electrons immediately start accumulating in the carbon coated on the foil
attached to the battery's negative terminal [see illustration, "Pluses and
Minuses"]. Those electrons, in turn, attract positive ions from the
electrolyte into the pores of the carbon on that foil. In the other
electrode, meanwhile, positive charges accumulate, attracting negative ions
from the electrolyte into the pores of the carbon. Both kinds of ions
migrate freely through the paper separator that prevents the electrodes from
touching each other and conducting current.
Notice that this so-called capacitor is actually a pair of capacitors in
series with each other. At each electrode, there is a separation of
charges-electrons and positive ions at the negative electrode, and positive
charges and negative ions at the positive electrode. So at each electrode
there are two layers of charge, which is why ultracapacitors are also known
as electric double-layer capacitors.
The activated carbon's huge surface area comes from the great porosity of
its microscopic nodules. It enables the positive and the negative ions
migrating through the electrolyte to find plenty of nooks and crannies to
occupy as they insinuate themselves as closely as possible into the
oppositely charged carriers inside the carbon. Basically, as an electrode
material, the activated carbon provides exactly the characteristics you want
for high capacitance: vast surface area and the opportunity for the
oppositely charged carriers to get atomically close to each other.
The surface area of the carbon varies, but 1500 square meters per gram is
not unusual. So for typical electrodes weighing 250 grams, the total area
would be 375 000 square meters-or roughly 50 soccer fields.
THE TRICK, OF COURSE, is getting that carbon onto the metal foil as
uniformly and efficiently as possible. It is the first step in NessCap's
manufacturing process-and the first topic of discussion on a tour of the
company's small but spotless factory. All manufacturing at NessCap goes on
in a series of three brightly lit rooms, whose Kelly green floors are all
marked with yellow lines to show visitors where to walk.
In big, shiny, stainless steel mixers-think Cuisinarts on
steroids-technicians mix several types of activated carbon with water and
with binding agents that cause the carbon-powder particles to stick to each
other and to the long strips of aluminum foil electrodes. The resulting
slurry gets coated onto one side of the aluminum, dried in a kiln, and then
coated onto the other side. After more drying, the coated strips are run
through a hot press to increase the density of their carbon layers and give
those layers a uniform thickness.
In the next room, machines scratch the carbon off the aluminum precisely and
at regular intervals to make places where electrical leads are attached.
Then the same machine winds together two long strips of the carbon-coated
metal-one will be the anode, the other the cathode-with a strip of paper in
between. "No other such machine exists in the world," says Inho Kim proudly.
In the third room, the wound electrode-separator assemblies are dried in a
kiln and inserted in aluminum cases that are filled with electrolyte and
welded shut. The finished capacitors are tested in a room across the hall;
every single capacitor is tested before leaving the factory.
Upstairs, NessCap's R&D department occupies a couple of rooms that take up
about the same total area as a decent restaurant kitchen. As in an old-time
apothecary, glass cabinets filled with bottles of powders and reagents line
Not surprisingly, ultracapacitor researchers are mainly interested in two
things: electrolytes and carbon. In virtually all high-performance
ultracapacitors, the electrolyte is acetonitrile. It's great stuff, in the
one way that really matters: it has terrifically low ionic resistance,
roughly 15 ohm-centimeters, and that means high power density. But when
acetonitrile burns, it can release cyanide, a fact that makes automakers
unhappy. "Everybody's looking for a replacement for acetonitrile," says
Burke at UC Davis. Several organic compounds, notably propylene carbonate,
show promise, but none at the moment has ionic resistance as low as
acetonitrile. (Honda used propylene carbonate in its own ultracapacitors, in
the FCX fuel-cell cars.)
Still, it is the carbon challenge that most consumes ultracapacitor
researchers now, because it is the key to the two main goals: getting costs
down and improving the energy (as opposed to power) density. In a typical
ultracapacitor, the electrode materials-the carbons, essentially-account for
more than half the cost of the device, Sun-wook Kim says.
During a tour of the laboratory, NessCap's R&D director, Young-ho Kim,
casually mentions that he's in the midst of running tests on no fewer than
10 mixtures of activated carbons, looking for a combination of low cost,
high performance, and durability that has so far eluded ultracapacitor
It all comes down to pores, he explains, drawing little circles on a piece
of paper. You want pores that are all about 20 to 30 angstroms in diameter.
Pores that are smaller than that aren't big enough to allow the ions to move
in and out freely, which hurts performance. Lots of big pores, on the other
hand, mean that the overall surface area is less than it should be, which
also limits performance.
Ultracapacitor makers are working with two main types of carbon,
phenyl-resin based and pitch based. Phenyl-resin carbons perform better and
are the standard now. But the attraction of pitch-based carbons, which are
derived from coke and are used in asphalt, is their low cost-about one-fifth
to one-tenth that of phenyl-resin carbons.
The problem, Young-ho Kim says, is that it's harder to control the pore-size
distributions in the pitch-based carbons, so they wind up with poorer
characteristics. Their capacitance is usually about 30 percent less than
that of the phenyl-resin-carbon devices, he explains. That means that 30
percent more material must be used, which, of course, detracts from the cost
savings and makes the finished devices larger. Still, Sun-wook Kim is
confident that work on the pitch-based carbons will be a key factor in
reducing the overall cost per farad of the devices.
In the next breath, though, he dismisses the conventional wisdom that the
carbons have to get down to $10 a kilogram to make ultracapacitors
cost-competitive, from about $100 today (for the phenyl-based carbons). He
insists that getting costs down will depend as much on manufacturing as on
carbon prices. He points out that NessCap is now changing its manufacturing
process to put its largest capacitors in cylindrical rather than rectangular
cans. The simple shape change allows the electrode assembly to be wound more
quickly, which in turn shaves more than 20 percent off the cost of making
the capacitors, Inho Kim estimates.
WHILE NESSCAP AND ITS COMPETITORS FOCUS on getting the cost of the carbons
down, a few other researchers are investigating exotic, pricey forms of
carbon that could eliminate the one clear drawback of ultracapacitors-low
energy density-and let them mount a serious challenge to batteries.
Commercially available ultracapacitors generally can be counted on to store
about 3 or 4 watthours per kilogram, Burke says. That's a far cry from the
60 or 70 Wh/kg typical of nickel-metal hydride batteries or the 110 to 130
Wh/kg delivered by lithium-ion batteries.
An ultracapacitor with batterylike energy density would be almost
irresistible to automakers, to say nothing of countless other manufacturers,
says John M. Miller, a retired Ford Motor Co. researcher. With high enough
energy density, ultracapacitors could reduce or even eliminate the need for
traction batteries in a hybrid car. "It's a pivotal time for energy-storage
systems," he concludes.
Tantalizing claims have surfaced of exotic carbon-based technologies that
could boost the energy density of ultracapacitors 10- or even 100-fold-well
into the realm of advanced batteries. But so far, these claims have not held
up to independent scrutiny, say both Burke and Marshall Miller at UC Davis.
An independent Japanese researcher, Michio Okamura, claims to have developed
a carbon-based electrode material that he calls nanogate, which is nonporous
and can deliver energy densities well above 50 Wh/kg. But solid, independent
verification of his claims is not yet available, according to Burke.
At MIT's electromagnetic laboratory, Schindall and lab director John
Kassakian, with Ph.D. student Riccardo Signorelli, are leading a project to
investigate the use of carbon nano-tubes, the latest miracle material, in
electrodes. They are creating materials in which the nanotubes grow out
perpendicularly from a substrate, like hair on a piece of scalp. The
nanotubes would become electrically charged, just as the activated carbon
does, so they would attract oppositely charged ions in the electrolyte. The
nanotubes would also be spaced so as to hold these ions, much as a sea
anemone grips small sea creatures in its tentacles. The advantage is that
this arrangement can in theory trap many more ions than even the pores of
activated carbon-enough perhaps to raise the energy density of an
ultracapacitor 100-fold, Schindall estimates.
So far, he and Signorelli have demonstrated technology that can grow the
right kind of nanotubes and space them appropriately. By next summer, they
hope to grow a patch of electrode big enough to test in an electrolyte, in
order to assess its capacitance characteristics. If it works as well as
their studies suggest, and if it can be easily manufactured-two big ifs-the
dream of a near-ideal energy storage device will be that much closer to
realization. "Suddenly, electrical energy storage turns on its
head-potentially," Schindall says.
MEANWHILE, FOR NESSCAP and its competitors, the game is basically this: find
enough niche markets to stay afloat until technology advances make
ultracapacitors even more attractive and automotive markets develop. And
NessCap isn't waiting for the niche markets to come to it. Last year, the
company started its own consumer-electronics firm, Infinity Inc., which is
selling everything from crank-powered radios to solar tiles, all outfitted
with NessCap capacitors.
NessCap is also working with several other companies on niche automotive
applications. A well-known courier company, for example, is about to start
using NessCap's ultracapacitors in 200 of its delivery vans. As they go
about dropping off packages in densely populated areas, these vans must stop
and restart their engines as many as 200 times a day. The short distances
between stops means that the starter batteries can't recharge sufficiently
and soon wear out. But the short distances are not a problem for
ultracapacitors, which recharge in seconds and can easily store enough
energy to fire up the engine. So the delivery-van system couples
ultracapacitors for short-term energy storage with lead-acid batteries for
Looking beyond these niche applications, Inho Kim has high hopes for
"micro-hybrids," which would have a 12-V battery, as in a conventional car.
Micro-hybrids are basically a very mild form of mild hybrid, propelled
mainly by a gasoline engine but with a beefed-up electric starter motor fed
by a small rack of ultracapacitors. The capacitors and motor provide the
stop-and-go operation described above; the car could also make use of
The guilt-free ultracapacitor-based roadster is probably more than a couple
of years away. But a conventional car with a more reliable starter system,
or even a micro-hybrid with an ultracapacitor boost, could be in your
immediate future. If so, the revolution in energy storage will be well under
TO PROBE FURTHER
Kilofarad International, a trade group formed to promote the ultracapacitor
industry, is an affiliate of the Electronic Components, Assemblies, and
Materials Association. Its Web site is at http://www.kilofarad.org
Andrew Burke of the University of California, Davis, has written numerous
technical articles on ultracapacitors. Several are available online,
including a survey from 2000:
Menahem Anderman, president of the consulting firm Advanced Automotive
Batteries, plans to release a report on ultracapacitors for automotive uses
in February. You can order the US $7200 report at