Ultracapacitor Technology Present and Future Performance and Applications_MIT

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Ultracapacitor Technology:

Present and Future Performance and Applications

Andrew Burke

Marshall Miller

Nathan Parker

Institute of Transportation Studies

University of California-Davis

Davis, California 95616

afburke@ucdavis. edu

IntroductionThis paper is meant to augment the materials and discussions given in a paper

(Reference 1) presented in August 2003 at the 2003 Capacitor Summit. In this paper, theemphasis is on testing of small ultracapacitor cells (10 F and 120F) and a 45V moduleconsisting of 3500 F devices and pulse charging and discharging with pulse durationsmuch smaller than the RC time constant of the cell. Projections are also made of furtherprogress in improving the energy density of ultracapacitors and their near-termapplications in both vehicle and stationary power systems.

Present Status of Ultracapacitor Technology

CellsCarbon/carbon devices

There are presently commercially available carbon/carbon ultracapacitor devices(single cells) from several companies Maxwell/Montena, Panasonic, Ness, and EPCOS.All these companies market large devices with capacitance of 1000-5000 F. Thesedevices are suitable for high power vehicle and stationary applications. The performanceof the various devices is given in Table 1. The energy densities (Wh/kg) showncorrespond to the useable energy from the devices based on constant power discharge

tests from V0 to V0. Peak power densities are given for both matched impedance and95% efficiency pulses. For most applications with ultracapacitors, the high efficiencypower density is the appropriate measure of the power capability of the device. For thelarge devices, the energy density for most of the available devices is between 3.5-4.5Wh/kg and 95% power density is between 800-1200 W/kg. In recent years the energydensity of the devices has been gradually increased for the carbon/carbon (double-layer)technology and the cell voltages have increased to 2.7V/cell using acetonitrile as theelectrolyte.


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Table 1: Summary of the Characteristics of Commercially Available

Carbon/Carbon Ultracapacitors

Device V

rated

C

(F)

R

(mOhm)

RC

(sec)

Wh/kg

(1)

W/kg

(95%)

(2)

W/kg

Match.

Imped.

Wgt.

(kg)

Vol.

lit.

Maxwell** 2.5 2700 .32 .86 2.55 784 6975 .70 .62

Ness 2.7 10 25.0 .25 2.5 3040 27000 .0025 .0015

Ness (3) 2.3 120 21.0 2.5 3.8 282 3700 .017 .010

Ness 2.7 1800 .55 1.00 3.6 975 8674 .38 .277

Ness 2.7 3640 .30 1.10 4.2 928 8010 .65 .514

Ness 2.7 5085 .24 1.22 4.3 958 8532 .89 .712

Asahi Glass

(propylene

carbonate)

2.7 1375 2.5 3.4 4.9 390 3471 .210

(estimated)

.151

Panasonic

(propylene

carbonate)

2.5 1200 1.0 1.2 2.3 514 4596 .34 .245

Panasonic 2.5 1791 .30 .54 3.44 1890 16800 .310 .245

Panasonic 2.5 2500 .43 1.1 3.70 1035 9200 .395 .328

EPCOS 2.5 220 3.0 .66 2.76 1126 10000 .052 .042

EPCOS 2.5 2790 .15 .42 3.46 2055 18275 .57 .377

Montena 2.5 1800 .50 .90 2.49 879 7812 .40 .30

Montena 2.5 2800 .39 1.1 3.33 858 7632 .525 .393

Okamura

Power Sys. 2.7 1350 1.5 2.0 4.9 650 5785 .21 .151

ESMA 1.3 10000 .275 2.75 1.1 156 1400 1.1 .547

(1) Energy density at 400 W/kg constant power, Vrated - 1/2 Vrated

(2) Power based on P=9/16*(1-EF)*V2/R, EF=efficiency of discharge

** Except where noted, all the devices use acetonitrile as the electrolyte

(3) Psuedo-caps from Ness using carbon/metal oxide electrodes

Psuedo-capacitive cells

As indicated in References (2-8), there have been considerable development ofultracapacitor devices that have at least one of the electrodes that utilize non-double-layermechanisms for electrical charge storage. Some of these devices use carbon in oneelectrode (References 2-5) and psuedo-capacitive or Faradaic processes in the otherelectrode. The characteristics of some of these technologies are given in Table 2.

Except for the Ness 120F device (Reference 8), these devices are not commerciallyavailable and are in varying stages of development and testing. In general, the energydensities of the psuedo-capacitive devices are significantly higher than the carbon/carbondevices and their power densities are lower. Also the energy densities of the psuedo-capacitive devices are more discharge rate dependent than those of the carbon/carbondevices. A major concern about the psuedo-capacitive devices is cycle and calendar lifeeven though the Ness 120F devices are claimed to have a cycle life of 100,000 deepdischarge cycles.

One of the most interesting ultracapacitor developments during the past year hasbeen work on carbon/carbon devices using graphitic carbon rather than activated carbon(References 6,7) done by Okimura and at Ahasi Glass. Charge is stored in the graphitic


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carbons by intercalation of the electrolyte ions into space between the carbon sheets aswith the Lithium ions in a Li-ion battery. The voltage of these devices are expected to bebetween 3 and 4V with energy densities of at least 20 Wh/kg. Their power densities

should be high, but probably not as high as carbon/carbon devices using activated carbon.

Table 2: Characteristics of various Psuedo-capacitor technologies

Device

Electrode

Materials Electrolyte

Voltage

Wh/kg/

Wh/L

(W/kg)

90% Status

Ness

Pseudo-

cap

Carbon/

metal oxide Organic 1.0-2.3

10/13 1000 Commercial

Okamura

Intercalation

into graphite

Organic 0-3.8 25/32

1200

Lab proto-

types

Ashasi

Glass

Intercalation

into a mix of

activated

carbon and

graphite

Organic 0-3.0 12/15 1200

Lab proto-

types

Telcordia LiTi/carbon Organic 1.0-2.8

14/24 1500

Lab proto-

Types

Atlantic

University,

Russians

Carbon/

NiOOH

Aqueous,

KOH 15/30 2000

Commercial

and small

lab devices

UC Davis,

Russians

Carbon/PbO2 Aqueous,

Sulfuric

Acid

1.0-2.1

15/40 3500 Small lab

cells

ModulesThere are presently several 42-45V modules (see Table 3) available consisting of

multiple, large ultracapacitor cells. For example, the Ness 45V module (Fig.1) consists ofeighteen (18) 3500 F devices connected in series with balancing circuits across the cells.As discussed in Reference 9, the Ness module was extensively tested at UC Davis and itsperformance was found to be close to that expected based on the characteristics of the

3500F cells. Constant power and PSFUDS data from those tests are given in Tables 4-5.Note that the power density of the module changes only by about 10% from low power tohigh power (744 W/kg) and the roundtrip efficiencies on the PSFUDS cycle are 95-96%.These characteristics result from the low resistance (6.5 mOhm) of the module.

As indicated in Table 3, the packaged weight and volume of the ultracapacitors inthe modules can be considerably greater than that of the cells alone resulting in lowpackaging factors. This is especially the case if provisions for cooling (fans and coolingchannels) are incorporated into the module. The density of carbon/carbon ultracapacitorcells is relatively low (1.2-1.3 gm/cm3) so unless considerable care is taken in packagingthe devices into a module the ultracapacitor unit will be unattractive to incorporate into a


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vehicle. Reasonable targets for packaging factors are .85 for weight and .7 for volumeexcluding cooling fans.

Figure 1: Photograph of the 45V Ness Ultracapacitor Module

Table 3: Characteristics of various 42-45V ultracapacitor modules

Module

Weight

(kg)

Volume

(liters) Voltage

Wh

Power(kW)

(90% effic.)

Weight

packaging

Factor

Volume

packaging

factor

Ness (1)

(194 F) 19.1 26.1 45 40 16.9 .635

.36

(with

cooling)

Maxwell(2)

(135 F)

16.0 22.0 42 25 8.5 .592 .32

(with

cooling)

Asahi

Glass (3)

(80 F)

6.1 5.4 42 15 2.2 Not avail.

.50

(without

cooling)

(1)tested at UC Davis (Reference 9)(2)tested at the Idaho National Engineering Laboratory

(3)specifications from References (7)


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Table 4: Constant Power Test Data for the Ness 45V module

Power

kW

Power density

(W/kg)*

Cycle

Energy

Wh

Energy density

(Wh/kg)*2 165 1 39.4 3.26

2 39.3 3.25

3 39.2 3.24

4 330 1 38.0 3.14

2 38.0 3.14

3 37.9 3.13

6 495 1 37.0 3.06

2 36.8 3.04

3 36.8 3.04

8 661 1 36.0 2.98

2 35.8 2.963 35.8 2.96

9 744 1 35.3 2.92

2 35.3 2.92

3 35.3 2.92

*energy and power density based on weight of the cells in the module

(weight of the cells is 12.1 kg)

Table 5: Roundtrip Efficiencies for the Ness 45V Module

on the PSFUDS cycle

Cycle*

Energy in

Wh

Energy out

Wh

Efficiency

%

1 102.84 97.94 95.2

2 101.92 97.94 96.1

3 101.67 97.94 96.3

*PSFUDS power profile based on maximum power of 500 W/kg

and the weight of the cells alone

Prospects for Future Improvements in ModulesFurther improvements in ultracap modules are needed in the following areas: (1)

cell performance, (2) packaging and cooling of the cells, (3) further development andtesting of balancing circuits that both reduce cell-to-cell variability of the voltage withcycling and do not increase cell self-discharge. The performance improvements(increased energy density Wh/kg and decreased resistance and hence maximum powerdensity) of ultracapacitor cells have been ongoing . For example, Ness (Reference 10) isprojecting that by 2005 the 3500 F device will have useable energy densities of 5.9Wh/kg and 6.8 Wh/liter and by 2009 the cell energy densities will be 8 Wh/kg and 8.4Wh/liter. Other ultracap manufacturers can be expected to make similar improvements inthe performance of carbon/carbon devices. These improvements in performance areprojected with further increases in power density and no sacrifice in the cycle life that isprojected to be greater than 500,000 deep discharge cycles. Cost will likely remain an


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issue, but with increasing volume of sales, it can be expected that device costs/prices willcontinue to decrease as has been the case in recent years.

There has been increasing research activity in hybrid ultracapacitors (References

2-7). These devices (see Table 2) have higher energy density than the carbon/carbondevices by a factor of 2-3. Presently the only hybrid device on the market is thePseudocap from Ness (Reference 8) that utilizes carbon on the negative electrode andlithium metal oxides on the positive. The largest Pseudocap marketed at the present timehas a capacitance of 120 F, but Ness plans to have 3500 F devices available by 2005which are projected to have energy densities of 9.1 Wh/kg and 11 Wh/liter. ThePseudocaps will have lower power and shorter cycle life than the carbon/carbon devices.The projected 90% discharge power of the Pseudocaps is about 1400 W/kg and the cyclelife about 100,000 cycles between 2.5 and 1V. The cost of the Pseudocaps will be lessthan that of the carbon/carbon devices by 15-20%.

As noted in Table 3, the modules currently available for use with 42V hybrid

systems have relatively low packaging factors. These modules incorporate air coolingfans which contribute significantly to their low packaging factors, especially the volumefactor. In the case of the Ness 45V module, if one eliminates the volume for the fans andthe air gap above the cells for cooling, the volumetric packaging factor increases from .36to .75. The weight factor will also increase, but it is more difficult to estimate. Hence ifthe cooling fans are provided external to the modules, the packaging factors for theultracapacitor modules can be expected to be reasonably high. For example, ininformation from Ness for a 144V system, they project weight packaging factors of .83and volume factors of .67. These factors are considerable higher than the correspondingfactors of .64 and .36 of the 45V module. Based on the result of removing the provisionfor the cooling fans from the 45V module, projected packaging factors of .85 and .70

seem reasonable as design targets for vehicle applicationsThe key function of the balancing circuit is protect the cells from over-voltage

when the module is charged to or maintained near its rated voltage. In principle, what isrequired is a balancing circuit that by-passes a small current during times of charging forthose cells that have a tendency to exceed a specified maximum voltage when the moduleis near its rated voltage (45V in the case of the Ness module). During times of dischargeand when the cell is kept well below the specified maximum voltage, the balancingcircuit should not effect the operation of the cell. Discussions with Ness indicated thenext generation balancing circuits will function in the manner just described and shouldnot significantly effect the self-discharge of the module (Reference 11, 12). Theseimproved balancing circuits should be available in the near term and improvement in the

performance of balancing circuits is not expected to be an issue in hybrid vehicleapplications of ultracapacitor modules. At the present time, the cost of the balancingcircuits is small compared to that of the capacitors, but their cost will be more of an issuewhen the cost of the capacitors is significantly reduced in future years.

Recent Tests of small Capacitor devices (10F carbon/carbon and

120F psuedo-cap devices)Constant current and constant power tests

The Ness 10F and 120F ultracapacitors (see Figure 2) were tested for appropriateranges of constant current and constant power. The data are shown in Table 6. The


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differences between the performance of the carbon/carbon and psuedo-cap devices areevident from the table. The energy density of the carbon/carbon device is significantlyless than that of the psuedo-cap at moderate powers, but the carbon-carbon device

maintains its energy density to very high power densities. The data also show that thecapacitance of the carbon/carbon device is essentially independent of current even at veryhigh current densities. It can be expected that these differences between the smallcarbon/carbon and psuedo-cap type devices will also remain true for larger devices (1000F). The advantages of the psuedo-cap or hybrid type devices are their higher energydensity and possible lower cost.

Figure 2: Photograph of the Ness 10 F carbon/carbon and 120F psuedo-

Cap devices

120F10F

Ness Pseudocapacitors


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Table 6: Summary of the constant current and constant power data

for the small Ness ultracapacitors

Ness 10F carbon/carbon Ness 120F Psuedo-capCurrent

(A)

Capacitance

(F)

Current (A) Capacitance

(F)

.5 10.6 .5 133

1.0 10.5 1.0 128

2.0 10.2 2.0 126

3.0 10.1 3.0 125

4.0 123

5.0 121

V0 = 2.7 V0 =2.3

Resistance = 25 mOhm Resistance=21 mOhm(from pulse tests)

10 F 120 F

Power

(W) W/kg Wh/kg

Power

(W) W/kg Wh/kg

.5 200 3.1 1 59 4.29

1.0 400 3.05 2 118 4.16

1.5 600 2.92 3 176 4.03

2.0 800 2.92 4 235 3.9

2.5 1000 2.90 6 353 3.26

3.0 1200 2.86 8 470 3.0210 588 2.79

Voltage: 2.7-1.35 Voltage: 2.3-1.0

Weight =2.5 grams Weight = 17 grams

Volume = 1.5 cm3

Volume = 10 cm3

Pulse charging and discharging tests

The 10 F and 120 F devices were also tested using pulse currents rather thansteady currents. The time durations of the current pulses were short compared to the RCtime constants of the devices. In the case of the 10 F device having a RC time constant

of .25 seconds, the pulse duration was .01 seconds with a repeat time of .05 seconds (dutycycle of 20%). For the 120 F device having a RC time constant of 2.5 seconds, the pulseduration was .05 seconds with a repeat time of .25 seconds (duty cycle of 20%). Theratio of time constant to pulse duration time was 25 for the 10 F device and 50 for the 120F device. The pulse charge/discharge profiles (voltage vs. time) for the two devices areshown in Figures 3 and 4. In both cases, the capacitance and resistance of the devicesdetermined


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Figure 3: Voltage vs. time trace for pulse charge/discharge of the

Ness 10 F carbon/carbon device

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0 100 200 300 400 500 600

Test_Time

Current

-0.5

0

0.5

1

1.5

2

2.5

3

Voltage

-6

-4

-2

0

2

4

6

0 100 200 300 400 500 600 700 800

Test_Time

Current

0

0.5

1

1.5

2

2.5

Voltage

Figure 4: Voltage vs. time trace for pulse charging/discharging of

120 F Ness psuedo-cap device


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from the pulse tests (see Table 7) were close to those determined from the steady DCcurrent tests even though the pulse durations were much smaller than the RC timeconstants. These tests indicate that ultracapacitors can be used in applications in which

the duration of the charge and discharge pulses are very short compared to the RC timeconstant of the devices without a loss of energy storage capacity.

Table 7: Pulse charging/discharging results for short duration pulses

Device Pulse duration RC/pulse Capacitance Resistance

10 F .01 sec 25 10.6 25 mOhm

120 F .05 sec 50 110 20 mOhm

Vehicle and Stationary Applications

Vehicle applications

During the last several years there has been an increasing recognition thatultracapacitors can be utilized as the energy storage component in electric and hybridvehicles. In a number of cases, demonstration programs involving the use ofultracapacitors have been undertaken with good results. In this section of the paper,vehicle applications of ultracapacitors will be identified and demonstration programsusing them briefly described.

One of the most near-term applications of ultracaps is to use them in combinationwith lead-acid batteries to start the diesel engines in large (Class 8) tractor-trailer trucks

(see reference 22). The ultracaps are especially advantageous in very cold, sub-zerotemperatures. Several companies are presently field testing ultracap/battery units beforeoffering them for sale.

Programs involving the use of ultracaps in electric vehicles are discussed inReferences 13, 14. In these programs, ultracaps are used to provide the power duringacceleration of the vehicles and to recover energy during braking. The ultracaps are thenrecharged from the batteries during periods of reduced electrical power demand. In thesevehicles, the power split between the ultracaps and the batteries was controlled withinterface electronics. The electrical drivelines functioned well as designed with theultracaps protecting the batteries from the high power surges in both discharge andcharge.

There are a number of examples in which ultracaps have been utilized in hybridvehicles. In these applications, ultracaps are used alone and in combination with batteries.Most of the vehicle demonstrations using ultracaps have been in heavy duty vehicles(buses and trucks) designed as series hybrids (References 15-17). In these vehicles, theultracaps are used to load level an engine/generator permitting it to operate with muchreduced transients and resultant lower emissions and higher fuel economy. The ultracapsalso permit the recovery of significant energy during braking in stop-go city driving.These programs have been quite successful with the ultracaps functioning as envisionedby the system designers.

In recent meetings there has been much discussion of the use of ultracaps inhybrid passenger cars (References 18-22). The application most discussed is the 42V


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stop/go hybrid utilizing a relatively low power electric drive (5-8 kW). In this case, theultracap could be combined with a lead-acid battery that would recharge the ultracap asneeded. The lead-acid battery would be recharged from the engine using either the

alternator or the traction motor as a generator. Systems utilizing this approach in hybridpassenger cars have been built and tested showing fuel economy gains of 10-15%(References 18-19). Ultracaps can also be used in high voltage, power assist mildhybrids replacing the nickel metal hybrid batteries. These designs utilize only slightlydown sized engines so that if/when the ultracaps become depleted the vehicles still hasgood performance. Recent simulation results for such systems are shown in Table 8taken from Reference 9. Using this approach, fuel economy increases of 30-40% arepossible with good vehicle acceleration performance.

Table 8: Fuel Economy Simulation (Advisor) Results using Batteries

and Ultracapacitors in Mild Hybrid Passenger Cars

Compact Car

Fuel economy mpg

Driving cycle Small cap

(94Wh)

Large cap

(180 Wh)

Ni mt.hydride

Battery

FUDS 44.1 44.4 40.2

Fed. HW 50.2 50.4 43.8

US 06 32.6 33.1 30.1

EC-EUDC 39.6 40.6 36.6

Mid-size Car

Fuel economy mpg


(150 Wh)

Large cap

(293 Wh)

Ni mt.hydride

Battery

FUDS 37.7 37.9 33.8

Fed. HW 43.3 43.5 37.3

US 06 29.7 29.8 26.1

EC-EUDC 35.4 35.4 30.7

Full-size Car

Fuel economy mpg


(210 Wh)

Large cap

(405 Wh)

Ni mt.hydride

Battery

FUDS 33.6 33.9 31.4

Fed. HW 37.4 37.6 34.1

US 06 24.9 25.0 23.7

EC-EUDC 30.9 31.2 28.4


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It has recently been recognized that ultracaps are especially well suited for usewith fuel cells (References 23-24) for the following reasons. First, unlike a battery, therest voltage of the ultracap is variable and not fixed by its chemistry resulting in easy

matching the fuel cell and ultracap voltages at rest (zero or minimum power draw).Second, the ultracap/fuel cell system is almost self-regulating without interfaceelectronics in that the fuel cell can only provide low power at high voltage when theultracap is nearly fully charged and will automatically provide high power at lowervoltage when the ultracap becomes depleted and needs to be recharged. Honda has usedultracaps in their fuel cell vehicles with great success (Reference 24) for a number ofyears and Hydrogenics (Toronto, Canada) is presently assembling and testing a fuel cellpowered neighborhood EV (GEM) and a fork-lift truck using ultracaps to provide thepower during periods of high power demand. The use of ultracaps with fuel cells tends tostabilize the fuel cell operation even during periods of rapidly changing electrical loadsand transients in hydrogen flow or purging.

Stationary applications

Many markets have been developing for ultracaps for non-vehicle or stationaryapplications. Most of these markets are related to consumer electronics, but some are forindustrial applications. In most cases, the applications utilize relatively small deviceswith capacitances less than 100 F. The markets are in the areas of cell phones, pagers,toys, audio boom boxes, lighting fixtures, wind turbine blade actuators, etc.

One of the markets that could use large ultracap devices that has been widelydiscussed is distributed UPS systems with engine/generators or fuel cells. Most of theUPS systems currently in use or being planned use lead-acid or nickel cadmium batteriesfor energy storage. These systems are designed for long outages of at least several hours.

However, with the recent power blackouts, there is much present interest in UPS systemsto cope with short periods (30 seconds or less) of high power demand or poor powerquality (Reference 25). These systems will require high power for short periods andrelatively small energy storage. Ultracaps should be ideal for use in such systems. Forexample, using the present technology for carbon/carbon devices, a 1000 kg, 750 literunit of capacitors could provide 3-4 MW of power for 6 seconds (5 kWh of energy). Itwould be impractical to use batteries for such short time UPS applications. Ultracaps canalso used with fuel cells in UPS systems to meet the starting transient when the system isactivated during a power outage.

Economic and Cycle life ConsiderationsWith the heightened recognition of the value of ultracaps in many applications,

the cost of the devices is the primary deterrent to their use or at least seriousconsideration in many advanced systems requiring electrical energy storage. The cost ofultracaps has been decreasing markedly over the last few years, but remains higher thancan be justified in many applications especially in vehicles. Present prices for largedevices appears to be 2-3 cents per farad. For a rated voltage of 2.7 V/cell, one cent perFarad corresponds to $15/Wh of useable energy. If the capacitor being considered has anenergy density of 5 Wh/kg and a power density of 1500 W/kg, $15/Wh corresponds to apower cost of $50/kW. If a target device cost for vehicles is $20/kW, this requires adevice cost of about .4 cents per Farad or about one-fifth (1/5) the present cost. This


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References1. Burke, A.F., Ultracapacitors: Present and Future, Proceedings of the Advanced

Capacitor World Summit 2003, Washington, D.C., August 20032 .Lipka, S.M., Reisner, D.E., Dai, J., and Cepulis, R., Asymmetric-Type

Electrochemical Supercapacitor Development under the ATP An Update,Proceedings of the 11

thInternational Seminar on Double Layer Capacitors

(Florida Atlantic University) , Deerfield Beach, Florida, Dec 2001.3. Amatucci, G.G., etals., The Non-Aqueous Asymetric Hybrid Technology:

Materials, Electrochemical Properties and Performance in Plastic Cells(Telcordia), Proceedings of the 11th International Seminar on Double-layerCapacitors, Deerfield Beach, Florida, December 2001.

4. Burke, A. F., Miller, M., and Kershaw, T., Feasibility Studies for theDevelopment of Hybrid Carbon/Lead Oxide Electrochemical Capacitors:Analysis, Assembly, and Test of Devices, UC Davis Report No. UCD-ITS-03-02,June 2003

5. Butler, S. A. and Miller, J. R., Asymmetric PbO2/H2SO4/C ElectrochemicalCapacitor, paper presented at the 203rdmeeting of the Electrochemical Society,Paris, France, April 2003

6. Takeuchi, M., Koike, K., Maruyame, T., Mogami, A., and Okamura, M.,Electrochemical Intercalation of Tetraethylammonium Tetrafluoroborate intoKOH-treated Carbon Consisting of Multi-Graphene Sheets for an ElectrochemicalCapacitor, Journal of the Electrochemical Society, 66, No. 12, pg 1311-1317,1998

7. Yoshida, N., Hiratsuka, K., and Ikeda, K., Design and Performance of AdvancedUltracapacitors, Asahi Glass, Proceedings of the Fourth International AdvancedAutomotive Battery Conference, San Francisco, Calif., June 2004

8. Kim, I., Ultracaps: Between EDLC and Pseudocapacitors, Proceedings of theAdvanced Capacitor World Summit 2003, Washington, D.C., August 2003

9. Burke, A, F., Ultracapacitor Module Technology for Use in Mild Hybrid ElectricVehicles, Proceedings of the Fourth International Advanced Automotive BatteryConference, San Francisco, Calif., June 2004

10.Kim, I., Private communication from Ness Capacitor Co. on future ultracapacitordevelopments, 2003

11.Jung, D.Y., Shield Ultracapacitor Strings from Overvoltage Yet MaintainEfficiency, Electronic Design, May 27, 2002

12.Kim, Y., Ultracapacitor Technology Powers Electronic Circuits, Power

Electronics Technology, October 200313.Wright, G., Jung, D.Y., Garabedian, H., On-road and Dynamometer Testing of a

Capacitor-Equipped Electric Vehicle, Proceedings of the 19th

InternationalElectric Vehicle Symposium, Busan, Korea, October 2002

14.King, R.D., Song, D., Gikakis,C., and Gilan, Y., Ultracapacitor Enhanced ZeroEmission Zinc-Air electric Transit Bus, Proceedings of the 20

thInternational

electric Vehicle Symposium, Long Beach, California, November 200315.Cannon, J., Scott, P., and Riegel, R., Hybrid-electric Fuel Cell Bus Demonstration,

Proceedings of the 20th International electric Vehicle Symposium, Long Beach,California, November 2003


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16.Espinosa, R., Allen, S., Arnet, B., Sghia-Hughes, K., and Tarnow, A.,Development of a Competitive Class 7 Hybrid Driveline, Proceedings of the 20 thInternational Electric Vehicle Symposium, Long Beach, California, November

200317.Okamuri, M., Buses, Trucks and FCVs using the Capacitor Hybrid System ECS,

Proceedings of the 19th International Electric Vehicle Symposium, Busan, Korea,October 2002

18.Bogel, W., Origuchi, M., and Hiron, C., DLC for Modern HEVs Optimization forPerformance, Size, and Cost, Proceedings of the Third International AdvancedAutomotive Battery Conference, Nice, France, June 2003.

19.Bachmeir, J., New Energy Storage Concepts for Mild Hybrid Vehicles,Proceedings of the fourth International Advanced Automotive Battery Conference,San Francisco, California, June 2004

20.Mitsui, K., Nakamura, H., and Okamuri, M, Capacitor-Electronic Systems (ECS)

for ISG/Idle Stop Applications, Proceedings of the 19th International ElectricVehicle Symposium, Busan, Korea, October 2002

21.Jung, D.Y., Kim, Y.H., and Choi, K.W., Ultracapacitor for 42 Volt AutomotiveElectrical System, Proceedings of the 19th International Electric VehicleSymposium, Busan, Korea, October 2002

22.Burke, A. F., Cost-effective Combinations of Ultracapacitors and Batteries forVehicle Applications, Proceedings of the Second International AdvancedAutomotive Battery Conference, Las Vegas, Nevada, February 2002

23.Burke, A.F. and Miller, M., Ultracapacitors and Fuel Cell Applications,Proceedings of the 20th International Electric Vehicle Symposium, Long Beach,California, November 2003

24.Oki, N., Application Studies of Electric Double-layer Capacitor System for FuelCell Vehicle, Proceedings of the 20

thInternational Electric Vehicle Symposium,

Long Beach, California, November 200325.Proceedings of the Electric Storage Conference: Gateway to a New World of

Reliable Power, Electric Storage Association 14th

Annual Meeting, Columbus,Ohio, May 2004

26.Deiml, M, Knorr, R., and Lugert, G., Mild Hybrid Going Wild-ISG providinghigh power for mild Hybrids enabling driving fun and reduced fuel consumption,Proceedings of the 20

thInternational Electric Vehicle Symposium, Long Beach,

California, November 2003 (Seimens)


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Ultracapacitor Technology Present and Future Performance and Applications_MIT