Electric Double Layer Capacitors (EDLC)

Anurag Yadav

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INTRODUCTION

Electric Double Layer Capacitors (EDLC) are also called super capacitors or ultra capacitors. They store energy in the form of static charges. EDLC resembles the ordinary capacitors but having high energy density. EDLC have very low working voltage ,and are used in hybrid vehicles. EDLC ‘s are rated from Farads to Kilo Farad ranges

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HISTORY & PRESENT

Electric double layer effect was first noticed by General Electric engineers in 1957. But this effect is rediscovered and researches are done by Standard oil of Ohio in 1966. But it is NEC,who finally marketted the result as SUPER CAPACTORS.

Due to the development of Material Science in 90’s,this technology improves rapidly. Today , electronic devices, Locomotives uses this technology.

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CONSTRUCTION

EDLC’s construction is a little different to that of ordinary capacitors. EDLC’s doesn't have any conventional dielectric rather than ,two plates separated by an inverting substance. The Super Capacitor uses plates of same material having same electrical properties and are called electric double layer.

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Main materials used for the construction are

Activated Charcoal CarbonNano Tubes Aerogels

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EDLC use Activated Charcoal as plates. It is because It’s a powder made of very small &

rough particle It’s having a low density particles with

holes Over all surface area is very much

larger than other materials like Al , Ti etc.

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But Activated Charcoal is not a perfect material for EDLC. It's because• The charge carriers are quite larger than the pores in the Charcoal . • Some times too large pore size in charcoal.

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Carbon Nano Tubes are used today.• They have same charge storage capability as that of Charcoal•Having much more mechanically arranged rigid pattern.•Having much more surface area.

PRINCIPLE & WORKING

EDLC store electrical charges similar to that of ordinary capacitors. But charges doesn't accumulate on electrode, instead it is stored in the interface between surface of the conductor and electrolytic solution.

Capacitance of EDLC is given by the equ: C= A ε / 4 π d A- Area of the contact plates d- distance between the plates ε – dielectric constant of the medium between the

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ELDC works on the process of double layer formed between electrode and electrolyte when a pd is applied.

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During charging, electrically charged ions in the electrolyte moves towards electrodes of opposite polarity due to electric field between charged electrode created by pd. Thus two charged plates are produced. This charged ions occupy spaces of the electrode and electrolyte which is separated by a very small distance. Due to large surface area large number of ions are formed ,

resulting highcapacitance.

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EQUIVALENT CIRCUIT

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ADVANTAGES

Eco friendly High Efficiency Rapid charging & Discharging Low internal Resistance High power density Reliable in harsh environment Virtually unlimited cycle life Simple charge methods

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Energy Density Vs Power Density

DISADVANTAGES

Unable to use full energy spectrum Low energy density High self discharge Low working voltage

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APPLICATIONS

UPS systems. Laptops. Regenerative breaking systems. Automotive: hybrid power trains and drive systems Consumer electronic devices that demand sudden energy

bursts for wireless communications, processing, and memory storage.

Industrial: applications requiring energy storage, bridging, delivery, and smooth transitioning.

Telecommunications : portable wireless devices, communication Satellites, cell towers, or off-the-grid electric power generation

Transportation : vehicles that frequently accelerate and brake use SC.

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BATTERY vs. CAPACITORS

Batteries Store energy by converting between

electrical and chemical energy Shelf life of a few years Not all are rechargeable

Capacitors Store energy as an electric potential

between two surfaces and a dielectric constant (ie. Aluminum)

Rechargeable Long shelf life Miniscule amount of energy loss during

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FUTURE SCOPES

Hybrid Battery The idea of replacing batteries with

capacitors in conjunction with novel alternative energy sources became a conceptual umbrella of “Green Electricity (GEL) Initiative, introduced by Dr. Alexander Bell.

Hybrid Battery is the one which have the properties of both capacitor and battery. High power density of caps and High energy density of battery is combine together

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Hybrid battery system is a new highly reliable energy storage device.

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CONCLUSION

This presentation deals with EDLC as an Energy storage device.The main advantage of this ELDCis ,Its having high power density, eco friendly, used in hybrid vehicles etc.

I hope ,new technologies in the material science & Nano will make this Super capacitor more advanced.

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