Supercapacitor

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Image:Maxwell supercapacitor MC2600 series 2600F.jpg

A supercapacitor or ultracapacitor is an electrochemical capacitor that has an unusually high energy density when compared to common capacitors. They are of particular interest in automotive applications for hybrid vehicles and as supplementary storage for battery electric vehicles.

1 History
2 Current State
3 Features
4 Technology
5 References
6 See also
7 External links
- 7.1 News

[edit] History

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

[edit] Current State

First trials of using the supercapacitors in industrial applications were carried out for supporting the energy supply to robots. [1]

In 2005 aerospace systems and controls company Diehl Luftfahrt Elektronik GmbH chose ultracapacitors Boostcap® (of Maxwell Technologies) to power emergency actuation systems for doors and evacuation slides in passenger aircraft, including the new Airbus 380 jumbo jet. [2]

In 2006, Joel Schindall and his team at MIT began working on a "super battery", using nanotube technology to improve upon capacitors. They hope to have a prototype within the next few months and put them on the market within five years. [3]

China is experimenting with a new form of electric bus that runs without powerlines using power stored in large onboard supercapacitors, which are quickly recharged whenever the electric bus stops at any bus stop. A few prototypes were being tested in Shanghai in early 2005.^{[citation needed]}

[edit] Features

Such energy storage has several advantages relative to batteries:

Very high rates of charge and discharge.
Little degradation over hundreds of thousands of cycles.
Good reversibility
Low toxicity of materials used.
High cycle efficiency (95% or more)

Disadvantages:

The amount of energy stored per unit weight is considerably lower than that of an electrochemical battery (3-5 W.h/kg for an ultracapacitor compared to 30-40 W.h/kg for a battery).
The voltage varies with the energy stored. To effectively store and recover energy requires sophisticated electronic control and switching equipment.
Has the highest dielectric absorption of all types of capacitors.

Image:Supercapacitors chart.svg

Image:Supercapacitor diagram.svg

[edit] Technology

Carbon nanotubes and polymers, or carbon aerogels, are practical for supercapacitors. Carbon nanotubes have excellent nanoporosity properties, allowing tiny spaces for the polymer to sit in the tube and act as a dielectric. Polymers have a redox (reduction-oxidation) storage mechanism along with a high surface area. MIT's Laboratory of Electromagnetic and Electronic Systems (LEES) is researching using carbon nanotubes<ref name = "MIT">MIT Lees on Batteries</ref>.

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

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

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