Supercapacitor
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 electric (including hybrid electric) vehicles and as supplementary storage for battery electric vehicles.
Contents |
History
The first supercapacitor based on a double layer mechanism was developed in 1957 by General Electric using a porous carbon electrode[1]. 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.[2]
Technology advantages
One of the earliest commercial-grade electronic devices powered by a single supercapacitor (a high-quality audio mixer) was described in the milestone article "Single capacitor powers audio mixer" authored by Aleksandr Belousov (EDN, March 14, 1997) [5]. A carefully designed circuit, which utilized micro-power amplifiers and farad-range supercapacitor (SuperCap or DynaCap), was capable of running for more than 2 hours on a single charge.
It also demonstrated, compared with rechargable batteries, the ultracharging (ability to be charged very quickly, in about ten seconds) as compared to the hours required for traditional rechargeable batteries. Due to the capacitor's high number of charge-discharge cycles (millions or more compared to 200–1000 for most commercially available rechargeable batteries) there were no disposable parts during the whole operating life of the device, which made the device very environmentally friendly. Other advantages of supercapacitors compared with rechargeable batteries are extremely low internal resistance or ESR, high efficiency (up to 97-98%), high output power, extremely low heating levels, and improved safety. According to ITS (Institute of Transportation Studies, Davis, CA) test results, the specific power of supercapacitors can exceed 6 kW/kg at 95% efficiency [3]
The idea of replacing batteries with capacitors in conjunction with novel alternative energy sources became a conceptual umbrella of the Green Electricity (GEL) Initiative [6], [7], introduced by Dr. Alexander Bell. One particular successful implementation of the GEL Initiative concept was introduced in the article: “Muscle power drives battery-free electronics” (Alexander Bell, EDN, 11/21/2005)[8], describing a muscle-driven autonomous, environmentally-friendly solution, which employs a multi-farad supercapacitor (hecto- and kilofarad range capacitors are now available) as an intermediate energy storage to power a variety of portable electrical and electronic devices such as MP3 players, AM/FM radios, flashlights, cell phones, and emergency kits. As the energy density of supercapacitors is bridging the gap with batteries, it is hoped that in the near future the automotive industry will start to deploy ultracapacitors as a replacement for chemical batteries [citation needed].
The first trials of supercapacitors in industrial applications were carried out for supporting the energy supply to robots. [4]
In 2005 aerospace systems and controls company, , 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. [5]
In 2006, Joel Schindall and his team at the MIT began working on a "super battery", using carbon nanotubes to improve upon capacitors. [6]
In 2006, United States Patent #7,033,406 [7] issued to EEStor for an electrical-energy-storage unit (EESU) using supercapacitors that can store 52 kW·h and weigh about 336 lb (152 kg). That would give it an energy/weight value of about 342 W·h/kg, twice that of lithium-ion batteries.
Transportation applications
China is experimenting with a new form of electric bus (capabus) that runs without powerlines using power stored in large onboard supercapacitors, which are quickly recharged whenever the electric bus stops at any bus stop (in the called electric umbrellas), and fully charged in the terminus. A few prototypes were being tested in Shanghai in early 2005. In 2006, two commercial bus routes began to use supercapacitor buses; one of them is route 11 in Shanghai. [8]
In 2001 and 2002, VAG, the public transport operator in Nuremberg, Germany tested a bus which used a diesel-electric drive system with supercapacitors.[9]
Since 2003 Mannheim Stadtbahn in Mannheim, Germany has operated an LRV (light-rail vehicle) which uses supercapacitors.[10] In this presentation[11], there is additional information about that project by the builder of the Mannheim vehicle, Bombardier Transportation, and the possible application of the technology for DMUs (Diesel Multiple Unit) trains.
Other companies from the public transport manufacturing sector are developing supercapacitor technology: The Transportation Systems division of Siemens AG is developing a mobile energy storage based on double-layer capacitors called Sibac Energy Storage [12]. The company Cegelec is also developing a supercapacitor-based energy storage system[citation needed].
Proton Power Systems has created the world's first triple hybrid Forklift Truck, which uses fuel cells and battery as primary energy storage and supercapacitors to supplement this overall energy efficient storage solution. [9]
Formula 1 Racing Application
The FIA proposed on May 23, 2007, in the Power-Train Regulation Framework for Formula 1, version 1.3, that a new set of power train regulations be issued that includes a hybrid drive of up to 200 kW input and output power, involving both batteries and supercapacitors.
Features
Supercapacitor 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 in first generation supercapacitors is considerably lower (1/10) than that of an electrochemical battery (3-5 W·h/kg for an ultracapacitor compared to 30-40 W·h/kg for a battery). It is also only about 1/10,000th the volumetric energy density of gasoline. Second generation (EEstor) are higher than lithium ion batteries.
- 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.
Technology
Carbon nanotubes and certain conductive 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. MIT's Laboratory of Electromagnetic and Electronic Systems (LEES) is researching using carbon nanotubes[13].
- Some polymers (eg. polyacenes) have a redox (reduction-oxidation) storage mechanism along with a high surface area.
- Supercapacitors are also being made of carbon aerogel. This is a unique material providing extremely high surface area of about 400-1000 m²/g. 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. Small aerogel supercapacitors are being used as backup electricity storage in microelectronics, but applications for electric vehicles are expected[14].
The capacitance of a single cell of an ultracapacitor can be as high as 3000 F (see photo at the beginning).
In August 2007, a research team at RPI (led by Drs. , Pulickel M. Ajayan, and ) developed a paper battery with aligned carbon nanotubes, designed to function as both a lithium-ion battery and a supercapacitor (called bacitor), using ionic liquid, essentially a liquid salt, as electrolyte. The sheets can be rolled, twisted, folded, or cut into numerous shapes with no loss of integrity or efficiency, or stacked, like printer paper (or a Voltaic pile), to boost total output. As well, they can be made in a variety of sizes, from postage stamp to broadsheet. Their light weight and low cost make them attractive for portable electronics, aircraft, automobiles, and toys (such as model aircraft), while their ability to use electrolytes in blood make them potentially useful for medical devices such as pacemakers. In addition, they are biodegradable.[15][16]
See also
References
- ^ US patent 2800616, "Low voltage electrolytic capacitor", granted 1957-07-23
- ^ US patent 3288641, "Electrical energy storage apparatus", granted 1966-11-29
- ^ APCT Prototype Test Results
- ^ http://www.maxwell.com/pdf/uc/app_notes/Peak_Load_Shaving-1007234.pdf
- ^ http://www.maxwell.com/news/release.asp?PRID=162
- ^ http://web.mit.edu/newsoffice/2006/batteries-0208.html , http://www.autoindustry.co.uk/news/16-04-07
- ^ Electrical-energy-storage unit (EESU) utilizing ceramic and integrated-circuit technologies for replacement of electrochemical batteries
- ^ [1]
- ^ [2]
- ^ UltraCaps win out in energy storage Richard Hope, Railway Gazette International July 2006
- ^ [3]
- ^ [4]
- ^ MIT LEES on Batteries
- ^ AIP
- ^ August 2007 Globe and Mail
- ^ http://news.rpi.edu/update.do?artcenterkey=2280
External links
- UltraCapacitors & SuperCapacitors
- Green Electricity Initiative: battery-free portable electronics (“GEL Initiative”), Alexander Bell, USA-Ultra-capacitors to replace batteries in portable equipment
- Mobile Electricity: Battery-free, renewable, clean (“GEL Initiative”), Alexander Bell, USA
- Single capacitor powers audio mixer, Alexander Bell, USA, EDN, March 14, 1997 -one of the earliest commercial grade Audio electronic solution powered by single Capacitor; was awarded as “Best Design Idea”
- Muscle power drives battery-free electronics, Alexander Bell, EDN, 11/21/2005 - Describes autonomous, cost-efficient and environmentally-friendly solution utilizing Ultra-capacitor in conjunction with alternative energy sources to power portable electronic equipment.
- Volumetric and Gravimetric Energy Density compared
- Ultracapacitor used in Honda's FCX fuel cell car
- Encyclopedia article on Electrochemical Capacitors
- Nano World: Carbon Nanotube Capacitors. Such nanoscale capacitors might help improve the development of compact and cost effective supercapacitors.
- Researchers fired up over new battery
- Business 2.0 profile of Texas company EEStor
- Good comparison of energy storage technologies.
- UltraCaps win out in energy storage; Double-layer capacitors have broken through the economic barriers to capturing braking energy on a Mannheim light rail vehicle.. Article from Railway Gazette International, July 2006.
- Bombardier MITRAC Energy Saver Light-rail vehicle and diesel-multiple unit applications for ultracapacitors.
- Ultracapbus in Nuremburg, Germany
- Siemens Sibac Energy Storage system
- Ultracapacitors combined with Photovoltaics for small-scale illumination
- Supercapacitors CNR-ITAE Messina Italy - Provides an overview of research activities in nanostructured materials for nanocapacitor applications at CNR-ITAE, Messina, Italy.
- Formula One 2011: Power-Train Regulation Framework
- The Dark Horse in the Race to Power Hybrid Cars Scientific American, August 28, 2007
- UltraCapacitors & SuperCapacitors - New Super Battery!