Supercapacitor Supercapacitor

A A supercapacitorsupercapacitor or or ultracapacitorultracapacitor is is an electrochemical an electrochemical capacitorcapacitor that has that has an unusually high an unusually high energy densityenergy density when when compared to common capacitors. They compared to common capacitors. They are of particular interest in automotive are of particular interest in automotive applications for applications for hybrid vehicleshybrid vehicles and as and as supplementary storage for supplementary storage for battery electric vehiclesbattery electric vehicles..

HistoryHistory

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

Current State Current State

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

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

The first trials of supercapacitors in industrial The first trials of supercapacitors in industrial applications were carried out for supporting the applications were carried out for supporting the energy supply to energy supply to robotsrobots. .

In In 20052005 aerospace systems and controls company aerospace systems and controls company Diehl Luftfahrt Elektronik GmbHDiehl Luftfahrt Elektronik GmbH chose chose ultracapacitors ultracapacitors Boostcap®Boostcap® (of (of Maxwell TechnologiesMaxwell Technologies) to power emergency ) to power emergency actuation systems for doors and actuation systems for doors and evacuation slidesevacuation slides in passenger aircraft, including the new in passenger aircraft, including the new Airbus 380Airbus 380 jumbo jet. jumbo jet.

In In 20062006, Joel Schindall and his team at , Joel Schindall and his team at MITMIT began began working on a "super battery", using nanotube working on a "super battery", using nanotube technology to improve upon capacitors. They hope technology to improve upon capacitors. They hope to have a prototype within the next few months to have a prototype within the next few months and put them on the market within five years. and put them on the market within five years.

Applications in Public Applications in Public Transport Transport

China is experimenting with a new form of China is experimenting with a new form of electricelectric bus bus that runs without powerlines using power stored that runs without powerlines using power stored in large onboard supercapacitors, which are quickly in large onboard supercapacitors, which are quickly recharged whenever the electric bus stops at any recharged whenever the electric bus stops at any bus stop, and get fully charged in the terminus. A bus stop, and get fully charged in the terminus. A few prototypes were being tested in Shanghai in few prototypes were being tested in Shanghai in early early 20052005. In . In 20062006, two commercial bus routes , two commercial bus routes began to use supercapacitor buses, one of them is began to use supercapacitor buses, one of them is route 11 in route 11 in ShanghaiShanghai. .

In 2001 and 2002, VAG, the public transport In 2001 and 2002, VAG, the public transport operator in operator in NuremburgNuremburg, Germany tested a bus which , Germany tested a bus which used a used a dieseldiesel--electricelectric drive system with drive system with supercapacitors supercapacitors

Since Since 20032003 Mannheim Stadtbahn in Mannheim, Mannheim Stadtbahn in Mannheim, Germany has operated an LRV (light-rail vehicle) Germany has operated an LRV (light-rail vehicle) which uses supercapacitors. In this presentation, which uses supercapacitors. In this presentation, there is additional information about that project there is additional information about that project by the builder of the Mannheim vehicle, by the builder of the Mannheim vehicle, Bombardier TransportationBombardier Transportation, and the possible , and the possible application of the technology for DMUs (application of the technology for DMUs (Diesel Multiple UnitDiesel Multiple Unit) trains.) trains.

Other companies from the public transport Other companies from the public transport manufacturing sector are developing manufacturing sector are developing supercapacitor technology: The Transportation supercapacitor technology: The Transportation Systems division of Systems division of Siemens AGSiemens AG is developing a is developing a mobile energy storage based on double-layer mobile energy storage based on double-layer capacitors called Sibac Energy Storage. The capacitors called Sibac Energy Storage. The company Cegelec is also developing a company Cegelec is also developing a supercapacitor-based energy storage system.supercapacitor-based energy storage system.

Features Features

Such energy storage has several Such energy storage has several advantages relative to advantages relative to batteriesbatteries::

Very high rates of charge and Very high rates of charge and discharge. discharge.

Little degradation over hundreds of Little degradation over hundreds of thousands of cycles. thousands of cycles.

Good reversibility Good reversibility Low toxicity of materials used. Low toxicity of materials used. High cycle efficiency (95% or more) High cycle efficiency (95% or more)

Disadvantages:Disadvantages:

The amount of energy stored per unit weight is The amount of energy stored per unit weight is considerably lower than that of an considerably lower than that of an electrochemical battery (3-5 W.h/kg for an electrochemical battery (3-5 W.h/kg for an ultracapacitor compared to 30-40 W.h/kg for a ultracapacitor compared to 30-40 W.h/kg for a battery). It is also only about 1/10,000th the battery). It is also only about 1/10,000th the volumetric energy density of gasoline.volumetric energy density of gasoline.

The The voltagevoltage varies with the energy stored. To varies with the energy stored. To

effectively store and recover energy requires effectively store and recover energy requires sophisticated electronic control and switching sophisticated electronic control and switching equipment.equipment.

Has the highest dielectric absorption of all types Has the highest dielectric absorption of all types

of capacitors. of capacitors.

Technology Technology

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

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

The electrodes of aerogel supercapacitors The electrodes of aerogel supercapacitors are usually made of non-woven paper are usually made of non-woven paper made from carbon fibers and coated with made from carbon fibers and coated with organic aerogel, which then undergoes organic aerogel, which then undergoes pyrolysis. The paper is a composite pyrolysis. The paper is a composite material where the carbon fibers provide material where the carbon fibers provide structural integrity and the aerogel structural integrity and the aerogel provides the required large surface.provides the required large surface.

The capacitance of a single cell of an The capacitance of a single cell of an ultracapacitor can be as high as 2.6 kF ultracapacitor can be as high as 2.6 kF (see photo at the beginning).(see photo at the beginning).