Super capacitors

Super capacitors

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  CONTENTS: • INTRODUCTION • CONSTRUCTION •WORKING • AEROGEL • WHY CARBON AEROGEL? • ADVANTAGES&DISADVANTAGES • APPLICATIONS • INNOVATIONS
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  INTRODUCTION • Definition: Supercapacitoris an electrical component capable of holding hundreds of times more electrical charge quantity than a standard capacitor. This characteristic makes them useful in devices that require relatively little current and low voltage. • Supercapacitor cells are able to fill the gap between conventional capacitors and batteries by providing high power performance in a compact design. • Supercapacitors are also known as Supercap, Pseudocapacitors, Gold Cap or Ultracapacitors, Electric Double-Layer Capacitor (EDLC).
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  CONSTRUCTION: • Supercapacitors areconstructed with two metal foils (current collectors), each coated with an electrode material like activated carbon. • The collectors serve as the power connection between the electrode material and the external terminals of the capacitor. • Both the electrodes are then separated by an ion permeable membrane(separator) used as an insulator to protect the electrodes against direct contact forcing short circuits. • This construction is subsequently rolled or folded into a cylindrical shaped aluminum can. 1.Terminals, 2.Safety vent, 3.Sealing disc, 4.Aluminum can, 5.Positive pole, 6.Separator, 7.Carbon electrode, 8.Collector, 9.Carbon electrode, 10.Negative pole
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  WORKING • Supercapacitors consistof two electrodes separated by an ion permeable membrane (separator), and an electrolyte connecting electrically the both electrodes. • By applying a voltage to the capacitor an electric double layer at both electrodes is formed, which has a positive or negative layer of ions deposited in a mirror image on the opposite electrode. 1. power source, 2. collector, 3.polarized electrode, 4. Helmholtz double layer, 5. electrolyte having positive and negative ions, 6. Separator.
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  Aerogel:  The mostcommonly used electrode material for supercapacitors is carbon aerogel.  Small pieces of cellulose nanofibers were trimmed, freeze- dried and then pyrolyzed at 1300 degrees Celsius under argon to convert the cellulose into ultralight nanofibrous carbon aerogel.  This substance has a density only one sixth of that of the air.
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  One of themajor interests in carbon aerogels is making electrical conductors with high surface areas. The equation that governs how much energy a capacitor can store is C = εA/d where C is the capacitance, ε is the dielectric constant of the separator between the plates, A is the surface area of the plates, and d is the distance between the plates. The larger A is in this equation, the more energy the capacitor can store-and for applications where infinitely-large plates are too cumbersome to carry around, high-surface-area conductors like carbon aerogels are very important materials. WHY CARBON AEROGEL?
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  Function Supercapacitor Lithium-ion(general) Charge time Cycle life Cell voltage Specific energy (Wh/kg) Specific power (W/kg) Cost per Wh Service life (in vehicle) Charge temperature Discharge temperature 1–10 seconds 1 million or 30,000h 2.3 to 2.75V 5 (typical) Up to 10,000 $20 (typical) 10 to 15 years –40 to 65°C –40 to 65°C 10–60 minutes 500 and higher 3.6 to 3.7V 100–200 1,000 to 3,000 $0.50-$1.00 (large system) 5 to 10 years 0 to 45°C –20 to 60°C
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  ADVANTAGES: DISADVANTAGES:  High powerdensity.  The supercapacitor can be charged and discharged virtually an unlimited number of times.  Under normal conditions, a supercapacitor fades from the original 100 percent capacity to 80 percent in 10 years.  Low impedance  No chemical actions.  Low energy density (6Wh/Kg).  High self discharge rate much higher than batteries.  Linear discharge voltage characteristic prevents use of all the available energy in some applications.  Power is available only for a very short duration.  Low cell voltage.
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  APPLICATIONS:  Power back-upfor memory functions in a wide range of consumer products such as mobile phones , laptops and radio tuners.  To provide fast acting short term power back up for UPS applications.  Energy storage for solar panels, and motor starters.  In camera flashes to enable discharging enough charge to produce a quick but bright flash of light.
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  INNOVATIONS:  China isexperimenting 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. In 2006, two commercial bus routes began to use supercapacitor buses, one of them is route 11 in Shanghai.  Recently in the university of California, a girl from India has invented a device made of super capacitor which charges the mobile phone battery in just 30 seconds.
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