Outline questions What is Capacitors? What are Supercapacitors? History of Supercapacitors. Advantages relative to Batteries Why they can store more energy, and why the mechanism of energy storage is so fast? Why supercapacitors? Disadvantage Applications.
What is Capacitor? A capacitor (originally known as condenser) is a passive two-terminal electrical component used to store energy in an electric field. When there is a potential difference (voltage) across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the form of electrostatic field.
What is 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 hybrid vehicles and as supplementary storage for battery electric vehicles
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.].
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).
Layman example for difference betweenSupercapacitor BatteryMore power required for small Constant but less power time interval in 200 m race required for large time in 20 km race
Specific power against specific energy Ragone plot
Electrochemical double layer capacitors (EDLC)• Store energy using ion adsorption (no faradaic (redox) reaction)• High specific surface area (SSA) electrodes (carbon) 100 – 120 F/g (nonaqueous electrolyte) 150 – 300 F/g (aqueous electrolyte)
Market Opportunity World Supercapacitors Market, $ mln. $560 mln. Obstacles to 600 500 grow 254.4 400 • Relatively high cost $272 mln. • Competition with batteries well established on 300 the market 89.6 161.4 • Consumer conservatism 200 111.4 100 0 70.8 144.8 Factors to growth 2006 2011 • New market opportunities like HEVs, Smart Grid, Alternative/Renewable Energy Electronics UPS and power tools Transportation • Growing ecology restrictions for competitorsFig. 5. Annual Sales divided by segments • Operation in a wide temperature range(Ultracapacitors - A Global Industry and MarketAnalysis, Innovative Research and Products , Inc. 2006) • Good prospects or a combined power supply
Why supercapacitors? Supercapacitors are known for over 50 years(patent of General Electric, 1957). Capacitance Supercapacitor are able to store and deliver of Earth isenergy at relatively high rates (beyond those 0.0007 Faccessible with batteries). A specific power of 5 000 W/kg can be reached. Supercapacitor exhibit very high degree ofreversibility in repetitive charge-discharge cycling.Cycle life over 500 000 cycles demonstrated.
Applications in Public Transport 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, and get 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. In 2001 and 2002, VAG, the public transport operator in Nuremburg, Germany tested a bus which used a diesel- electric drive system with supercapacitors .
Since 2003 Mannheim Stadtbahn in Mannheim, Germany has operated an LRV (light-rail vehicle) which uses supercapacitors. In this presentation, 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. The company Cegelec is also developing a supercapacitor-based energy storage system.
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).
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. Some polymers (eg. polyacenes) have a redox (reduction-oxidation) storage mechanism along with a high surface area. MITs Laboratory of Electromagnetic and Electronic Systems (LEES) is researching using carbon nanotubes .
Supercapacitors are also being made of carbonaerogel. Carbon aerogel is a unique materialproviding extremely high surface area of about400-1000 m2/g. Small aerogel supercapacitorsare being used as backup batteries inmicroelectronics, but applications for electricvehicles are expected.
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).
Disadvantage 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). It is also only about 1/10,000th the volumetric energy density of gasoline. 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.
Applications: Maintenance free applications Public transportation, HEVs, Start-Stop System Back-up and UPS systems Systems of Energy Recuperation Consumer electronics