brief history of supercapacitors

AUTUMN 2007 • Batteries & Energy Storage Technology 61

H I S T O RY O F T E C H N O L O G Y

A brief history ofsupercapacitorsIt took 150 years for a concept established in the 1800sto become a technical reality, and a further two decadesto make it commercially available. John Miller explainshow today’s electrochemical capacitors evolved fromhumble beginnings.

Robert A. Rightmire, a chemist at the Standard OilCompany of Ohio (SOHIO), to whom can beattributed the invention of the device in the for-mat now commonly used. His patent (U.S.3,288,641), filed in 1962 and awarded in lateNovember 1966, and a follow-on patent (U.S.Patent 3,536,963) by fellow SOHIO researcherDonald L. Boos in 1970, form the basis for themany hundreds of subsequent patents and jour-nal articles covering all aspects of EC technology.

This technology has grown into an industrywith sales worth severalhundred million dollarsper year. It is an industrythat is poised today forrapid growth in the nearterm with the expansionof power quality needsand emerging trans-portation applications.

Following the com-mercial introduction ofNEC’s SuperCapacitor in1978, under licencefrom SOHIO, ECs haveevolved through severalgenerations of designs.

Initially they were used as back-up powerdevices for volatile clock chips and complemen-tary metal-oxide-semiconductor (CMOS) comput-er memories. But many other applications haveemerged over the past 30 years, includingportable wireless communication, enhancedpower quality for distributed power generationsystems, industrial actuator power sources, andhigh-efficiency energy storage for electric vehicles

An electrochemical capacitor (EC), oftencalled a Supercapacitor or Ultracapacitor,stores electrical charge in the electric dou-

ble layer at a surface-electrolyte interface, prima-rily in high-surface-area carbon. Because of thehigh surface area and the thinness of the doublelayer, these devices can have very a high specificand volumetric capacitance. This enables them tocombine a previously unattainable capacitancedensity with an essentially unlimited charge/dis-charge cycle life. The operational voltage per cell,limited only by thebreakdown potential ofthe electrolyte, is usually<1 or <3 volts per cellfor aqueous or organicelectrolytes respectively.

The concept of stor-ing electrical energy inthe electric double layerthat is formed at theinterface between anelectrolyte and a solidhas been known sincethe late 1800s. The firstelectrical device usingdouble-layer chargestorage was reported in 1957 by H.I. Becker ofGeneral Electric (U.S. Patent 2,800,616).Unfortunately, Becker’s device was impractical inthat, similarly to a flooded battery, both elec-trodes needed to be immersed in a container ofelectrolyte, and the device was never commer-cialised.

Becker did, however, appreciate the largecapacitance values subsequently achieved by

“The uniqueattributes of ECs

often complementthe weaknesses of

other power sourceslike batteries and

fuel cells.”



plete account of this early work was presented byDon Boos, one of the SOHIO chemists involvedin the project, at a conference in 1991 called ‘AnInternational Seminar on Double Layer Capacitorsand Similar Energy Storage Devices’.

In this presentation Boos described the dis-covery of the phenomenon and the early activityin developing practical devices. One accountdescribed the difficulty in obtaining stable electri-cal readings on fuel cells that often took a goodpart of a morning to reach steady-state operation.The length of time was attributed to charge actu-ally being stored in the device. This led to theconcept of using a pair of high-surface-area car-bon electrodes to create an energy storagedevice. The product was referred to at the time asan ‘Electrokinetic capacitor’, and SOHIO provid-ed samples of commercial prototypes to manyparts of the market.

Figure 1 shows the cover of a brochure of 25April 1969 used for marketing and sampling theElectrokinetic capacitor. The introductory page isshown in Figure 2.

Work at SOHIO was eventually gearedtowards developing a replacement for aluminiumelectrolytic capacitors. This was before the timethat ‘keep alive’ memory back-up applicationsexisted, i.e. it was long before CMOS memory ordigital clock chips. Power rectification filteringwas identified as the market, and considerableeffort went into trying to develop or optimise theproduct for this application. It is interesting thatsome developers still have this as a goal today,

The original pamphlet describing the supercapacitor concept.

(EVs) and hybrid electric vehicles (HEVs).Overall, the unique attributes of ECs often com-plement the weaknesses of other power sourceslike batteries and fuel cells.

Early ECs were generally rated at a few voltsand had capacitance values measured from frac-tions of farads up to several farads. The trendtoday is for cells ranging in size from small milli-farad-size devices with exceptional pulse powerperformance up to devices rated at hundreds ofthousands of farads, with systems in some appli-cations operating at up to 1,500 volts. The tech-nology is seeing increasingly broad use, replacingbatteries in some cases and in others comple-menting their performance.

This article presents historical informationabout the development of EC technology and theapplications this technology is used in.Information sources include technical publica-tions, news releases, product brochures and per-sonal communications. Information will not beprovided for every EC ever developed, given thatsome developers were or are very small with onlyniche-market products, or have only recentlyentered the market.

1962: ELECTROCHEMICAL CAPACITORS ATSOHIOCarbon double-layer capacitors originated withpractical devices developed by SOHIO. Workbegan in the early 1960s as an outgrowth of fuelcell-related development activity. A fairly com-

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Having rapidly developed manufacturing capabil-ity, NEC began pre-production of the FA series in1978. These were sampled for many differentpotential applications. Mass production followedin January 1980. In 1982 sales of EC products withdifferent optimisations (i.e. new model series)began. Many other product models were intro-duced in the 1980s to meet new applicationrequirements.

One unique feature of the NEC capacitordesign was bipolar construction. NEC developedprocesses to stack six or eight cells in series in abipolar arrangement and successfully seal theentire device. This is significant because this sim-ple construction eliminates the need for cell inter-connects. (The same approach has been subse-quently used by several other companies, notablyECOND and ELIT, in their very large high-powercapacitors.)

NEC reported development of much largerdouble-layer capacitors in 1991, using an activat-ed carbon composite electrode. Because of theiressentially rigid electrodes, these devices did notrequire high compression for good performance.In 1996 the product brand name was changed toTokin. Several new products were introduced inthe 1990s, including the FG series, the highpower FT series, and the FC series. In 2001 a spi-ral-wound series and a low-profile thin-formatseries, both having organic electrolyte, appeared.The brand name was changed from Tokin toNEC-Tokin in 2002. Figure 3 shows some of theEC product series produced by NEC-Tokin.

NEC has certainly been one of the leaders inthe technology over the past 30 years, with a richhistory of developing and marketing EC products.Indeed, it is the only company that makes a true‘Supercapacitor’.

1975: ELECTROCHEMICAL CAPACITORS ATECONDIn December 1993 Dr Alexander Ivanov present-ed a paper at the Third International Seminar onDouble Layer Capacitors and Similar EnergyStorage Devices that described ECs much largerin size than devices available in the U.S. or Japan.Dr Ivanov’s company, ECOND, was located inMoscow and had ties with the Russian Ministry ofRailroads. He described large capacitors beingused to start 3,000 horsepower diesel locomotiveengines. These capacitors not only stored a largeamount of energy, but they were also some of themost powerful reported up to that time.

The ECOND ‘PSCap’, as the devices arecalled, uses a bipolar construction with an aque-

some 30 years later – a goal still not satisfactorilymet using double-layer charge storage technology.

Because SOHIO was heavily in debt frombuilding the Alaska pipeline, in 1971 it made cutsin many long-term development programmes,including the capacitor project. They had not yet,however, licensed the technology. The firstlicensee failed to commercialise the technologyand the licence reverted back to SOHIO.

The second licensee was Nippon ElectricCompany (NEC) of Japan. Starting in 1975 NECcarried out fundamental investigations, rapidlydeveloped manufacturing capability, and beganto market the ‘Supercapacitor’ in 1978. It is forthis reason that the only appropriate use of theterm Supercapacitor is for NEC’s EC products.These were aimed primarily at the emergingCMOS memory back-up application and at clockchip back-up, providing back-up power for thesedevices in VCRs, clock radios, microwave ovensand similar consumer electronic goods.

After oil began flowing through the Alaskapipeline in 1977 SOHIO resumed its capacitordevelopment activities. The ‘Maxcap’ double-layer capacitor product was introduced in theearly 1980s, having an aqueous electrolyte andbipolar construction, and rated up to severalfarads and 5.5 volts. With consolidation in the oilindustry, ownership of the Maxcap product lineshifted first to Carborundum, then to Cesiwid,and finally to Kanthal Globar.

1975: ELECTROCHEMICAL CAPACITORS ATNECNEC began its fundamental investigations in 1975after licensing the technology from SOHIO.

Figure 3: NEC – Tokin capacitors.



ous electrolyte. The design is a cylinder aboutnine inches in diameter and, depending on thestored energy, from several inches up to morethan two feet in height. Energies range from afew kilojoules up to 45kJ for the PSCap used inlocomotive engine starting. Equivalent seriesresistances of modules are typically in the mil-liohm range. Module voltages up to 200 volts arecommon. The RC-time-constant of the PSCap is afraction of a second, considerably less than thatof most previous products.

The 1993 Ivanov paper was an eye-opener forcapacitor developers at the meeting, especiallywith the projected need at that time for a 1.8MJload-levelling energy storage system for use inelectric vehicles. The achievements reported werea significant step ahead of research reported inthe U.S. and Japan, and provided significantencouragement for many capacitor developers inthe West.

In a recent letter to me, Dr Ivanov relatedsome of the obstacles he faced in his early capac-itor research activity, which started in the mid1970s. A 1974 Report of the USSR Academy ofSciences contained the paper ‘AnomalousElectrical Capacity and Experimental Models ofHyperconductivity’ describing a molecular capac-itor. Much scepticism was expressed—both bythe Academy and by the Government – about thistype of storage technology, referred to as ‘molec-ular energy storage’. Nevertheless developmentfunds were granted, but with very close over-sight. This work eventually led to the develop-ment in 1980 of a kV-rated, MJ-sized capacitorsystem, followed shortly by a ‘Government StatePremium’ award to the researchers responsiblefor this achievement.

Beginning in 1985, development effortsfocused on transportation applications related

primarily to internal combustion engine starting.The ECOND Corporation was created in 1991 tocommercialise the technology under Dr Ivanov’sdirection. Since 1994 ECOND capacitor productshave been used in many U.S. demonstration sys-tems, like diesel truck starting, as well as in HEVs.An article in the Spring 2007 issue of BESTdescribes several of these demonstrations. Figure 4shows one of the first gas-electric hybrid city tran-sit buses to use capacitor energy storage – 1.6MJ of200 volt PSCap modules. These capacitors are alsoavailable through a Canadian distributor.

1978: ELECTROCHEMICAL CAPACITORS ATPANASONICPanasonic began manufacturing its ‘Goldcap’double-layer capacitors in Japan in 1978. Thesewere initially developed primarily to replace theunreliable coin cell batteries used in memoryback-up applications at that time. The major dif-ferences between the Panasonic and NEC prod-ucts were the electrolyte and the fact that NECused an aqueous electrolyte in a ‘pasted elec-trode’ with bipolar cell construction, whilePanasonic used a nonaqueous electrolyte in anon-pasted electrode in the cell construction. Thenonaqueous electrolyte offered the advantage ofhigher unit cell operating voltage. The non-past-ed electrode in the Goldcap allowed Panasonic toproduce ECs without obtaining a licence fromSOHIO.

Panasonic developed two distinct designs.One was a coin cell, used to replace battery-typecoin cells; the second was a spiral-wound config-uration, similar to that of an aluminium EC. Theinitial Panasonic product had a voltage rating ofapproximately 1.8 volts per cell, a considerablestep up from the cell voltage of NEC products.This meant that for the 5.5 volt rating popular at

Figure 4: One of the first hybrid city transit buses using capacitor energy storage.




cles. Subsequent advances increased the energyin that same size product from 470F to 800F.

In 1999 Panasonic introduced the ‘UpCap’capacitor, rated at 2,000F and 2.3 volts, for trans-portation applications including HEVs. Thedevice is very well engineered, with a sophisti-

cated double seal for preventing water entry intothe package that is a much lower-cost arrange-ment than welded construction. It has essentiallycontinuous tabbing of the spiral foils at each end,which helps reduce series resistance, as well as

the time of introduction only three series-con-nected cells would be required, rather than thesix series-connected cells required using NEC’scomparable Supercapacitor.

In the mid 1980s Panasonic manufactured but-ton-cell capacitors in several different sizes: one-half farad, two-thirds farad,and so on. These became verypopular for solar-poweredwrist watches. The advantageof using a capacitor in thatapplication was that it did nothave the life limitations of abattery and could therefore besealed into the watch duringmanufacturing, eliminating theneed for a battery-replace-ment cover seal which mightleak. The watch was generallycharged from an amorphoussilicon photovoltaic materiallocated around the perimeterof the watch face. Chargingtook several minutes in directsunlight or several hours inweak room light. The coin cellcapacitor stored sufficientenergy to operate the watchfor 24 hours or longer (in darkness).

Panasonic began manufacturing much largerEC prototypes in the 1990s. These were spiralwound and rated at 470F, 2.3 volts or 1,500F, 2.3volts. The former of these were extensively test-ed for possible use in load-levelling electric vehi-

Figure 5: The performance improvements in Panasonic Goldcap capacitors.

Figure 6: A cut-through of ELIT’s first asymmetric EC.


helping to extract any internally generated heat.This is important for the repetitive charge/dis-charge cycles of hybrid vehicles, including regen-erative braking in stopping and acceleration afterthe stop. Figure 5 shows the historic size trendsof the Panasonic Goldcap EC cells.

1988: ELECTROCHEMICAL CAPACITORS ATELITIn early 1993 Alexey Beliakov, Technical Directorfor MP Pulsar in Kursk, Russia, sent a reader’s let-ter to Batteries International. He wanted to cor-rect information in an earlier issue by pointingout the existence of his company’s large ECs. Hepresented pictures of very large capacitors, 30and 50kJ, rated for 12 and 24 volts, used forengine starting. He described the testing done onthese devices and talked about delivery of a600kJ set of capacitors. Capacitors of this size andsophistication were totally unheard of in the U.S.at that time.

MP Pulsar changed its name to ELIT.Development of the ELIT capacitor began in 1988at the Accumulator Plant in Kursk. A year later thedevelopers had created the first asymmetric EC,one based on a nickel oxyhydroxide positiveelectrode, potassium hydroxide electrolyte, andan activated carbon negative electrode. Thesedevices were designed to power wheelchairs and,subsequently, children’s cars. ELIT’s emphasisshifted in 1990 to symmetric designs with potas-sium hydroxide electrolyte and two activated car-bon electrodes. Its capacitors use bipolar con-struction and a prismatic form factor, as shown inthe cutaway in Figure 6.

Modules with voltages as high as 400 voltsand capacitor sets of 1,500 volts can be produced,although nominal 12 and 24 volt modules forvehicle applications are more common. The ELITcapacitor is very powerful, having an RC-time-constant of a small fraction of a second. ELIT hasdeveloped an automated and flexible productionline (Figure 7), currently with a production capa-bility of more than 250,000kJ of capacitors peryear. ELIT sells large numbers of ECs in Russiaand has sold over 30,000 in the U.S.

1989: ELECTROCHEMICAL CAPACITORS ATELNA Elna, in collaboration with Asahi Glass of Japan,developed and began selling several styles of theirorganic electrolyte Dynacap EC in the U.S. startingin the late 1980s. Elna produces coin cells and spi-ral wound products, some with the same packagesize and ratings as the Panasonic Goldcap. They

do, however, make several families of capacitorcells quite different from Panasonic’s, in sizes upto 200F and rated at 2.5 volts. One of its productlines is very powerful, with RC-time-constantsbetween 0.1 and 1 second, depending on size,and it has developed and commercialised an ECcell with a 3.0 volt rating.

At the Centennial Meeting of theElectrochemical Society in 2002 Asahi Glass’s DrT. Morimoto described an asymmetric EC with anintercalation electrode paired with a double-layercharge storage electrode, both electrodes beingcarbonaceous and using an organic electrolytecontaining a lithium salt. The energy density ofunpackaged prototypes was reported to be 16Wh/l. Today several groups are advancing thisand similar approaches, because of both the high-er operating voltage (4.2 volts) offered and theresulting higher energy density provided – per-haps twice that of symmetric carbon-carbon ECs.Commercial production of capacitors with thisasymmetric design is imminent.

1991: ELECTROCHEMICAL CAPACITORS ATMAXWELL Before 1991 Maxwell Technologies of San Diego,California had developed a broad line of high-voltage capacitor products used in many of theearly magnetic fusion machines and other high-energy-density applications of the time, like laserflash-lamp power supplies. In 1991 the companywas awarded a contract by the U.S. Departmentof Energy (DoE) to develop advanced ECs, inresponse to a broad-area request by DoE in 1990for EC development proposals.

The goal was a technology suitable for load

Figure 7: ELIT’s production line in Russia.


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were then wound into cylindrical cells. Maxwell has developed a broad family of EC

products called BoostCaps. Cells range in sizefrom a small hermetically packaged 5F cell,through the wound 350F D-cellí size to the verylarge 3,000F, 2.7 volt rated tubular cells having aseries resistance of <0.3 mW (figure 8). Packagingfor the larger-size components is well engineeredusing penetration-weld attachment techniques toelectronically bond the spiral-wound current col-lectors to the package terminals and thus providelow series-resistance and very effective heatextraction. The larger devices are being used inmany applications, including HEVs, distributedgeneration systems like wind turbines, and inter-nal combustion engine starting modules.

Maxwell licensed its technology to EPCOS inGermany in the 1990s. (EPCOS elected to exit thismarket in late 2006, reportedly due to the antici-pated length of time predicted before profitabilitywas achieved.) In conclusion, MaxwellTechnologies has grown into the leading U.S. pro-ducer of ECs clearly aimed for the world market.

1993: ELECTROCHEMICAL CAPACITORS ATESMA In December 1997 Dr Arkadiy Klementov deliv-ered a presentation titled ‘Application ofUltracapacitors as Traction Energy Sources’ at theSeventh International Seminar on Double LayerCapacitor and Similar Energy Storage Devices. Heshowed photographs of buses and trucks poweredsolely by ECs: no batteries, no gas engines. Somein the audience missed the point that such heavyelectric vehicles were powered solely by capaci-tors. This was the first disclosure in the West ofcapacitor systems of such large size and of capac-itors with energy densities exceeding 10 Wh/kg.The capacitor bank used for propulsion in thetrucks and buses could store about 30 MJ of ener-gy at 190 volts. The invention that ESMA created tostore energy for these traction applications was anasymmetric capacitor (U.S. patent 6,222,723 andearlier Russian patents). This design essentiallyuses one battery electrode mated with a double-layer charge storage (capacitor) electrode. Thecombination offers certain advantages over thestandard, more common symmetric design. Theseinclude higher specific energy, higher operatingvoltage for an aqueous electrolyte, lower materialscosts since the charge storage carbon effectivelyhas twice the capacitance, and voltage self-balanc-ing in high-voltage strings of capacitor cells. Thesefour advantages are extremely important in manyof today’s applications.

levelling a battery storage system in EVs. Itincluded a capacitor that would store 500 Wh(1.8MJ) of energy, be capable of delivering 50kWof power, operate at 300 volts, weigh less than100kg, and have a specific energy greater than 5Wh/kg. Additionally the materials costs for thisenergy storage system were to be less than$1,000. This initial DoE specification provided thebasis for the Maxwell development programme,and it served likewise as a guide for many otherdevelopers of EV load-levelling capacitors.

Maxwell worked jointly with AuburnUniversity in capacitor development. The tech-nology that they initially chose was a metal-car-bon fibre composite electrode with aqueouspotassium hydroxide electrolyte. The metal fibreswere initially nickel, sintered to carbon fibres.The idea was to reduce the electronic resistancethat had been observed in some electrodes madewith particulate forms of carbon and also to takeadvantage of the shape of a single fibre asopposed to more sphere-like carbon particles.Eventually Maxwell changed its design to anorganic electrolyte and also changed the materialfrom nickel-carbon to aluminium-carbon cloth,with the intention of improving specific perform-ance. In the mid 1990s Maxwell’s EC develop-ment efforts moved from the Auburn facility toSan Diego.

In 2002 Maxwell purchased the EC manufac-turer Montena Components of Rossens,Switzerland. Rapidly this led to several productchanges that included replacing the accordion-folded, metallised carbon cloth electrode materialpreviously used in the larger cells with carbon-coated aluminium foil current collectors which

Figure 8: A Maxwell Boostcap.




The Joint Stock Company ESMA (of Troitsk,Russia) was created in 1993 for the developmentand manufacture of ECs. The systems that ESMAhas developed range in size from small 20kJ, 14volt modules up to very large 190 volt, 30MJ sys-tems used to power buses and trucks. Cells rangein size from 3,000F to more that 100,000F. Cellconstruction is similar to that used in aircraft NiCdbatteries but with activated carbon substituted forcadmium in the negative electrode. The ESMAcells are flooded, have the ability to reach voltagebalance naturally in series strings, and offer verygood power performance with high cycle life.

The design offers very favourable cost advan-tages over organic electrolyte products, sincematerial purity issues are not as important, mate-rials and package drying is unnecessary, and her-metic (welded metal) packaging is not needed.However the nickel foil used for the current col-lectors has, like most metals in the recent past,become very expensive, negating some of thesecost advantages.

ESMA has at least three capacitor optimisa-tions: pulse capacitors, which are intended fordischarges of a few seconds or less like enginestarting; intermediate-power capacitors, like thoseneeded in hybrid vehicles; and traction capaci-tors, designed to power electric vehicles like forklifts, utility vehicles, trucks and buses. Generallythese traction devices can be charged in 12 to 15minutes and discharged during one or morehours of operation. Several U.S. demonstrationprojects using ESMA capacitors have been report-ed, including an uninterruptible power supply(UPS) that delivered 100kW for ten seconds.

ESMA and its business partner AmericanElectric Power (AEP) have reported advancesmade in a significantly lower-cost lead oxide/sul-phuric acid/activated carbon asymmetric EC atthe recent 2007 Advanced Capacitor WorldSummit. They are developing this technology tostore large amounts of electricity from the utilitygrid at night, when there is abundance, for useduring the next day, when it may be in short sup-ply. Night storage/day use like this would involveonly a single cycle per day, some 365 cycles in ayear – a small number indeed. A storage systemdesigned to last for ten years would require nomore than 5,000 cycles, a number readily achiev-able with asymmetric ECs but a real stretch formany battery systems.

The recent ESMA paper also reported goodcycle efficiency, with an estimated cycle lifegreater than 5,000 cycles. The energy density ismuch higher than that of symmetric ECs, and it

approaches, although it is still less than, that oflead-acid batteries. Figure 11 shows a photographof one of these day/night storage capacitor pro-totypes that has been optimised for a charge/dis-charge cycle of five hours charging and five hoursdischarging. Figure 12 is a concept drawing thatwas presented by the DoE three years ago for acapacitor system that provides 1MW for fivehours. Presently it is the economics of such sys-tems that determine their viability, any questionsabout technological feasibility appearing alreadyto have been answered.

1994: ELECTROCHEMICAL CAPACITORS ATCAP-XXIn 1994 Commonwealth Scientific & IndustrialResearch Organization (CSIRO) of Australiaentered into a partnership with Plessey Ducon, amanufacturer of passive components, to evaluate

Figure 9: A charge/discharge curve for an ESMAsupercap designed for electric utility use.

Figure 10: A concept drawing of capacitor-based energystorage system.


1995: ELECTROCHEMICAL CAPACITORS ATNIPPON CHEMI-CONNippon Chemi-Con (NCC) of Japan is a billion-dollar manufacturing company that has earnedthe distinction of having the largest slice of theworld aluminium electrolytic capacitor market. Sowhen NCC introduced its DLCAP EC product linein the U.S. at the 2005 Advanced Capacitor WorldSummit, uncertainty about the long-term viabilityof large EC components instantly evaporated.NCC described products that had been optimisedfor either energy or for power, and presented testdata that strongly suggested NCC had consider-able prior experience with this technology.

Indeed they had – more than ten years of ECresearch and development activity dating back towork with Isuzu Motors in 1995. The time-lineshown in Figure 14 charts the advance of thetechnology. NCC prototype production began in1997 and mass production in 1998, with both spi-ral wound and prismatic cells being made, thelargest having a 3,000F, 2.5 volt rating.

The DLCAP is unique in several respects. First,it is built on the many years of related materials,packaging and manufacturing experience thatNCC acquired from the aluminium electrolyticcapacitor business it began in 1931. This degreeof vertical integration is unmatched in the ECindustry. Second, NCC uses a propylene carbon-ate solvent in its electrolyte that does not have thefire and health issues associated with some of thealternative organic electrolytes. And third, trulyunderstanding the cost issues of mass productionand recognising that practical limitations on mate-rial purity will lead ECs to generate some gas dur-ing operation that can lead to package swelling,NCC incorporated the innovative pressure-regu-lating valve in the DLCAP package (shown in

Figure 15). The valve serves thepurpose of releasing any generat-ed gas that may build up to a low,yet specified, pressure – whetherit arises from normal operation orfrom abuse conditions like theapplication of excessive voltageor over-temperature. Note thatthis resealable valve approach isonly feasible with nontoxic elec-trolytes.

Most petroleum used in Japanis imported, making energy con-servation very important to thecountry. Thus many of the pres-ent NCC EC applications relate tocapturing, storing and re-using

EC technology and itsmarket potential. Twoyears later the develop-ment team produced ahigh-energy-density car-bon and organic elec-trolyte capacitor capableof storing up to 9 Wh/kg,with time constants rang-ing from seconds to mil-liseconds. These devicesused spiral-wound singlecell construction.

In 1997 Cap-XX PtyLtd was formed to devel-op small high-powerdevices for the mobilecomputing and wirelessmarkets. It has built acommercial productionfacility and now manufac-tures a series of varioussmall size, very high-

power capacitors.These have a flat pris-matic profile andemploy minimal pack-aging, as shown inFigure 13. They are

constructed without the use of welding or glass-to-metal seals. Typical products include pairs ofseries-connected cells rated at 4.5 volts, with capac-itance in the range 0.12F to 0.8F. ESR on all theseproducts is 0.1 ohm or less, and RC-time-constantsare as short as 20ms. These small components areamong the most powerful ECs on the market,intended for pulse-power portable electronics mar-kets like digital wireless communication.

Figure 12: NCC supercaps showing an improving performance trend.



Figure: 11 Australian Cap XX device. One of the smallest and most powercomponents on the market.

energy that normally would be wasted as heat.An example is seaport gantry cranes used to loadand unload container ships (Figure 16): energystored while lowering a container is subsequent-ly re-used to assist in lifting the next one.

Reported energy savings fromusing DLCAP energy storage is40% over a conventional system.Similar levels of savings havebeen achieved with other indus-trial equipment having repetitiveback-and-forth or up-and-downmotion.

1998: ELECTROCHEMICALCAPACITORS AT NESSCAPThe NessCap EC was initiallycreated from technology spun

off from the Daewoo Group of Korea. Starting upin 1998 with both public and private funding,NessCap rapidly developed capacitor manufactur-ing capability and a broad product line of ECs.NessCap products use an organic electrolyte withspiral wound prismatic cell construction. Its firstcommercial shipment of capacitors to the U.S.market was in mid 2000.

NessCap currently makes cells from a fewfarads to 5,000F in size, and some of them arerated at 2.7 volts, among the highest voltage inthe industry. The larger capacitor cells have pris-matic packages for efficient stacking in modules.NessCap recently introduced a product line of 42volt modules for the automotive market.Applications for NessCap capacitors are broadand range from transportation to power quality.Figure 17 is a photograph of a 5,000F NessCapEC.

NessCap has also developed a complementa-ry high-energy-density line of EC products basedon pseudocapacitance charge storage. Thesedevices have a single-cell design like the compa-ny’s double-layer capacitor products, offer energydensity advantages, but have lower cycle life. Apopular application for these components is insolar-powered lighting as in light-emitting tiles,road studs and garden lights. In these electricitygenerated by solar cells is stored in the pseudo-capacitor and used at night to power LEDs in thesystem.

SUMMARY We can characterise the 30-year history of EC tech-nology perhaps best as one of continual break-through development, in which initial cost chal-lenges have consistently led to innovations thatnot only meet cost concerns but open up newavenues of discovery. Electrochemical capacitortechnology still has many miles to go in terms oftechnical promise and practical applicability.

Figure 13: The DL Cap from Nippon Chemicon showing its releasevalve.

Figure 14: NessCap capacitor module rated at5,000 farads.

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brief history of supercapacitors

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