Supercapacitors store energy through a double-layer capacitance mechanism and have a higher energy density than traditional capacitors. They were first developed in 1957 and store energy in the interface between porous carbon electrodes and an electrolyte. Supercapacitors can charge and discharge rapidly, undergo hundreds of thousands of cycles with little degradation, and are being researched for applications in electric vehicles and transportation where high power is required. While they currently have lower energy density than batteries, advances in materials like carbon nanotubes and aerogels may help bridge this gap.

1. SupercapacitorSupercapacitor

3. AA supercapacitorsupercapacitor oror ultracapacitorultracapacitor is anis an
electrochemicalelectrochemical capacitorcapacitor that has anthat has an
unusually highunusually high energy densityenergy density whenwhen
compared to common capacitors. Theycompared to common capacitors. They
are of particular interest in automotiveare of particular interest in automotive
applications forapplications for hybrid vehicleshybrid vehicles and asand as
supplementary storage forsupplementary storage for
battery electric vehiclesbattery electric vehicles..

4.  HistoryHistory
 The first supercapacitor based on a double layerThe first supercapacitor based on a double layer
mechanism was developed inmechanism was developed in 19571957 by General Electricby General Electric
using a porous carbon electrode [Becker, H.I., “Lowusing a porous carbon electrode [Becker, H.I., “Low
voltage electrolytic capacitor”,voltage electrolytic capacitor”, U.S. Patent 2800616U.S. Patent 2800616, 23, 23
July 1957]. It was believed that the energy was stored inJuly 1957]. It was believed that the energy was stored in
the carbon pores and it exhibited "exceptionally highthe carbon pores and it exhibited "exceptionally high
capacitance", although the mechanism was unknown atcapacitance", although the mechanism was unknown at
that time. It was thethat time. It was the StandardStandard Oil CompanyOil Company, Cleveland, Cleveland
(SOHIO) in(SOHIO) in 19661966 that patented a device that storedthat patented a device that stored
energy in the double layer interface [Rightmire, R.A.,energy in the double layer interface [Rightmire, R.A.,
“Electrical energy storage apparatus”,“Electrical energy storage apparatus”,
U.S. Patent 3288641U.S. Patent 3288641, 29 Nov 1966.]., 29 Nov 1966.].

5. Current StateCurrent State
 One of the earliest commercial-grade Electronic solutions poweredOne of the earliest commercial-grade Electronic solutions powered
by a single SuperCapacitor (a high-quality Audio mixer) wasby a single SuperCapacitor (a high-quality Audio mixer) was
described in the milestone article "described in the milestone article "Single capacitor powersSingle capacitor powers
audio mixeraudio mixer " authored by Alexander Bell (EDN, March 14, 1997)." authored by Alexander Bell (EDN, March 14, 1997).
A carefully designed circuit, which utilized micro-power amplifiersA carefully designed circuit, which utilized micro-power amplifiers
and Farad-range supercapacitor (SuperCap™ or DynaCap™) wasand Farad-range supercapacitor (SuperCap™ or DynaCap™) was
capable of running for more than 2 hours on a single charge. It alsocapable of running for more than 2 hours on a single charge. It also
demonstrated the ability to be charged very fast (in about tendemonstrated the ability to be charged very fast (in about ten
seconds) compared to the hours required for traditionalseconds) compared to the hours required for traditional
rechargeable batteries. Due to the capacitor's high number ofrechargeable batteries. Due to the capacitor's high number of
charge-discharge cycles (millions or more compared to 200-1000 forcharge-discharge cycles (millions or more compared to 200-1000 for
most commercially available rechargeable batteries) there were nomost commercially available rechargeable batteries) there were no
disposable parts during the whole operating life of the device, whichdisposable parts during the whole operating life of the device, which
made the solution very environmentally friendly.made the solution very environmentally friendly.

6.  The idea of replacing batteries with capacitors in conjunction withThe idea of replacing batteries with capacitors in conjunction with
novel alternative energy sources became a conceptual umbrella ofnovel alternative energy sources became a conceptual umbrella of
““Green Electricity (GEL) InitiativeGreen Electricity (GEL) Initiative , introduced by Dr., introduced by Dr.
Alexander Bell. One particular successful implementation of theAlexander Bell. One particular successful implementation of the
“GEL Initiative” concept was introduced in the article: ““GEL Initiative” concept was introduced in the article: “MuscleMuscle
power drives battery-free electronicspower drives battery-free electronics ” (Alexander Bell, EDN,” (Alexander Bell, EDN,
11/21/2005), describing muscle-driven autonomous,11/21/2005), describing muscle-driven autonomous,
environmentally-friendly solution, which employs a multi-Faradenvironmentally-friendly solution, which employs a multi-Farad
supercapacitor (hecto- and kilo-Farad range capacitors are nowsupercapacitor (hecto- and kilo-Farad range capacitors are now
widely available) as intermediate energy storage to power thewidely available) as intermediate energy storage to power the
variety of portable electrical and electronic devices (MP3 players,variety of portable electrical and electronic devices (MP3 players,
AM/FM radios, flashlights, cell-phones, emergency kits, etc.). As theAM/FM radios, flashlights, cell-phones, emergency kits, etc.). As the
energy density of supercapacitors (or ultracapacitors - these twoenergy density of supercapacitors (or ultracapacitors - these two
terms can be used interchangeably) is bridging the gap withterms can be used interchangeably) is bridging the gap with
batteries, it could be expected that in the near future the automotivebatteries, it could be expected that in the near future the automotive
industry will implement ultracapacitors as a replacement forindustry will implement ultracapacitors as a replacement for
chemical batteries.chemical batteries.

7. The first trials of supercapacitors in industrial applicationsThe first trials of supercapacitors in industrial applications
were carried out for supporting the energy supply towere carried out for supporting the energy supply to
robotsrobots..
 InIn 20052005 aerospace systems and controls companyaerospace systems and controls company
Diehl Luftfahrt Elektronik GmbHDiehl Luftfahrt Elektronik GmbH chose ultracapacitorschose ultracapacitors
Boostcap®Boostcap® (of(of Maxwell TechnologiesMaxwell Technologies) to power) to power
emergency actuation systems for doors andemergency actuation systems for doors and
evacuation slidesevacuation slides in passenger aircraft, including the newin passenger aircraft, including the new
Airbus 380Airbus 380 jumbo jet.jumbo jet.
 InIn 20062006, Joel Schindall and his team at, Joel Schindall and his team at MITMIT beganbegan
working on a "super battery", using nanotube technologyworking on a "super battery", using nanotube technology
to improve upon capacitors. They hope to have ato improve upon capacitors. They hope to have a
prototype within the next few months and put them onprototype within the next few months and put them on
the market within five years.the market within five years.

8. Applications in Public TransportApplications in Public Transport
 China is experimenting with a new form ofChina is experimenting with a new form of electricelectric busbus
that runs without powerlines using power stored in largethat runs without powerlines using power stored in large
onboard supercapacitors, which are quickly rechargedonboard supercapacitors, which are quickly recharged
whenever the electric bus stops at any bus stop, and getwhenever the electric bus stops at any bus stop, and get
fully charged in the terminus. A few prototypes werefully charged in the terminus. A few prototypes were
being tested in Shanghai in earlybeing tested in Shanghai in early 20052005. In. In 20062006, two, two
commercial bus routes began to use supercapacitorcommercial bus routes began to use supercapacitor
buses, one of them is route 11 inbuses, one of them is route 11 in ShanghaiShanghai..
 In 2001 and 2002, VAG, the public transport operator inIn 2001 and 2002, VAG, the public transport operator in
NuremburgNuremburg, Germany tested a bus which used a, Germany tested a bus which used a dieseldiesel--
electricelectric drive system with supercapacitorsdrive system with supercapacitors

9.  SinceSince 20032003 Mannheim Stadtbahn in Mannheim,Mannheim Stadtbahn in Mannheim,
Germany has operated an LRV (light-rail vehicle) whichGermany has operated an LRV (light-rail vehicle) which
uses supercapacitors. In this presentation, there isuses supercapacitors. In this presentation, there is
additional information about that project by the builder ofadditional information about that project by the builder of
the Mannheim vehicle,the Mannheim vehicle, Bombardier TransportationBombardier Transportation, and, and
the possible application of the technology for DMUs (the possible application of the technology for DMUs (
Diesel Multiple UnitDiesel Multiple Unit) trains.) trains.
 Other companies from the public transportOther companies from the public transport
manufacturing sector are developing supercapacitormanufacturing sector are developing supercapacitor
technology: The Transportation Systems division oftechnology: The Transportation Systems division of
Siemens AGSiemens AG is developing a mobile energy storageis developing a mobile energy storage
based on double-layer capacitors called Sibac Energybased on double-layer capacitors called Sibac Energy
Storage. The company Cegelec is also developing aStorage. The company Cegelec is also developing a
supercapacitor-based energy storage system.supercapacitor-based energy storage system.

10. FeaturesFeatures
 Such energy storage has severalSuch energy storage has several
advantages relative toadvantages relative to batteriesbatteries::
 Very high rates of charge and discharge.Very high rates of charge and discharge.
 Little degradation over hundreds ofLittle degradation over hundreds of
thousands of cycles.thousands of cycles.
 Good reversibilityGood reversibility
 Low toxicity of materials used.Low toxicity of materials used.
 High cycle efficiency (95% or more)High cycle efficiency (95% or more)

11. Disadvantages:Disadvantages:
 The amount of energy stored per unit weight isThe amount of energy stored per unit weight is
considerably lower than that of an electrochemicalconsiderably lower than that of an electrochemical
battery (3-5 W.h/kg for an ultracapacitor compared to 30-battery (3-5 W.h/kg for an ultracapacitor compared to 30-
40 W.h/kg for a battery). It is also only about 1/10,000th40 W.h/kg for a battery). It is also only about 1/10,000th
the volumetric energy density of gasoline.the volumetric energy density of gasoline.
 TheThe voltagevoltage varies with the energy stored. To effectivelyvaries with the energy stored. To effectively
store and recover energy requires sophisticatedstore and recover energy requires sophisticated
electronic control and switching equipment.electronic control and switching equipment.
 Has the highest dielectric absorption of all types ofHas the highest dielectric absorption of all types of
capacitors.capacitors.

12. TechnologyTechnology
 Carbon nanotubesCarbon nanotubes and certainand certain
conductive polymersconductive polymers, or carbon, or carbon aerogelsaerogels, are, are
practical for supercapacitors. Carbon nanotubespractical for supercapacitors. Carbon nanotubes
have excellent nanoporosity properties, allowinghave excellent nanoporosity properties, allowing
tiny spaces for the polymer to sit in the tube andtiny spaces for the polymer to sit in the tube and
act as a dielectric. Some polymers (eg.act as a dielectric. Some polymers (eg.
polyacenespolyacenes) have a redox (reduction-oxidation)) have a redox (reduction-oxidation)
storage mechanism along with a high surfacestorage mechanism along with a high surface
area. MIT's Laboratory of Electromagnetic andarea. MIT's Laboratory of Electromagnetic and
Electronic Systems (LEES) is researching usingElectronic Systems (LEES) is researching using
carbon nanotubescarbon nanotubes [1].[1].

14.  Supercapacitors are also being made ofSupercapacitors are also being made of
carbon aerogel. Carbon aerogel is acarbon aerogel. Carbon aerogel is a
unique material providing extremely highunique material providing extremely high
surface area of about 400-1000 m2/g.surface area of about 400-1000 m2/g.
Small aerogel supercapacitors are beingSmall aerogel supercapacitors are being
used as backup batteries inused as backup batteries in
microelectronics, but applications formicroelectronics, but applications for
electric vehicles are expected.electric vehicles are expected.

16.  The electrodes of aerogel supercapacitors areThe electrodes of aerogel supercapacitors are
usually made of non-woven paper made fromusually made of non-woven paper made from
carbon fibers and coated with organic aerogel,carbon fibers and coated with organic aerogel,
which then undergoes pyrolysis. The paper is awhich then undergoes pyrolysis. The paper is a
composite material where the carbon fiberscomposite material where the carbon fibers
provide structural integrity and the aerogelprovide structural integrity and the aerogel
provides the required large surface.provides the required large surface.
 The capacitance of a single cell of anThe capacitance of a single cell of an
ultracapacitor can be as high as 2.6 kF (seeultracapacitor can be as high as 2.6 kF (see
photo at the beginning).photo at the beginning).