introduction to supercapacitors

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INTRODUCTION TO SUPERCAPACITORS

JIBIN RAJU II MSc PHYSICS CUSAT

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OUTLINEIntroductionBasic designApplicationsAdvantagesDisadvantagesConclusionsReferences

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IntroductionCAPACITORS A capacitor (originally known as condenser) is a

passive two-terminal electrical component used to store energy in its electric field.

When a capacitor is attached across a battery, an electric field develops across the dielectric, causing positive charge +Q to collect on one plate and negative charge −Q to collect on the other plate

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SUPERCAPACITORS A supercapacitor is an electrochemical capacitor that has

an very high energy density as compared to common capacitors, about 100 times greater

Supercapacitor is also known as Electric Double Layer Capacitor(EDLC) or Ultra capacitor.

The capacitance range is from 100 Farad to 10KFarad.

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HISTORY OF SUPERCAPACITORSIn 1950s General Electric Engineers started

experimenting components using porous carbon electrodes for fuel cells and rechargeable batteries.

In 1957 H. Becker developed a "Low voltage electrolytic capacitor with porous carbon electrodes".

That capacitor came to known as Supercapacitor as it stored very high amount of energy.

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BASIC DESIGN

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Electrochemical capacitors (supercapacitors) consist of two electrodes separated by an ion permeable membrane (separator), and an electrolyte electrically connecting both electrodes. When the voltage is applied, ions in the electrolyte form electric double layers of opposite polarity to the electrode's polarity.

------------

++++++++

++

++++ +

+

Electrolyte

Separator

Electric double layer

▬ +

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TYPES OF SUPERCAPACITORS Different types of supercapacitors, based on the type of

electrode are as follows.I. Electrochemical double-layer capacitors (EDLCs): Have activated carbon electrodes or derivativesNo charge-transfer, non FaradaicAdvantages: Higher energy density than conventional capacitors,

comparable power densities, greater cycle stability Disadvantage:Cannot match energy density of mid-level batteries

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II. Pseudocapacitors:1. Have metal oxide or conducting polymer electrodes2. Ions diffuse into pores, undergo fast, reversible surface

reactions(REDOX Reactions)

Advantage: Higher energy density & capacitance than EDLCs Disadvantages: Lower power density than EDLCs, limited life cycle,

expensive electrode material

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III. Hybrid Capacitors: Combine the advantages & less disadvantages of the first

2 types 3 types of electrodes: composite, asymmetric, battery-typeAdvantages:Most flexible performance, high energy and power density

without sacrifices in cycling stabilityDisadvantages:Relatively new and unproven, more research required

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c. Hybridcapacitor

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Charge storing mechanismElectric Double Layer Capacitor

AEDL formed with electrode and electrolyte with solvent molecules between as dielectric. Store energy by adsorbing electrolyte ions onto the surface of the electrode

Fast acting. Low energy potential, charge confined to surface

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Pseudocapacitor

Rely on redox reactions that take place at the electrode.

Electrode materials typically made up of transition metals, conducting polymers, or compound with O and N functional groups.

Higher Energy density but lower cycling life.

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Hybrid capacitorsA combination of EDLC and pseudocapacitors. Optimizes power density of EDLC with energy density of pseudocapacitor.

One common example is the Li ion capacitor which is a current leader in the field.

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Application In start up mechanism for Automobiles. Supercapacitors are suitable temporary energy storage

devices. Supercapacitors provide backup or emergency shutdown

power to low-power equipment. e.g., ups.

They used in industrial lasers, medical equipment.

Large supercapacitors are used in wind turbines.

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Advantages relative to Batteries:Very high rates of charge and discharge.

Little degradation over hundreds of thousands of cycles.

Wide working temperature

Good reversibility.

Low toxicity of materials used.

High cycle efficiency (95% or more).

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Supercapacitor Battery

Layman example for difference between

More power required for small time interval in 200 m race

Constant but less power required for large time in

20km race

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Disadvantages Individual cells have low voltages, and so series

connections are needed to obtain higher voltages.

Having high self – discharge rate.

 Cannot be used in AC and high frequency circuits.

Cost is high.

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ConclusionsSupercapacitors may be used where high power or energy

storage is required that it will replace the batteries for power storage.

Supercapacitors can be used widely because of their long life & short charging time.

On the other hand it has limitations due to its high cost, self discharge, packaging problems etc.

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ReferencesAvinash Balakrishnan, K. R. V. Subramanian, “Nanostructured

Ceramic Oxides for Supercapacitor Applications”, CRC press 2013

Manisha Vangari,Tonya Pryor, and Li Jiang, “Supercapacitors: Review of Materials and Fabrication Methods” 2013

Simon, Patrice, Yury Gogotsi, and Bruce Dunn. “Where Do Batteries End and Supercapacitors Begin?” Science 343, no. 6176 (March 14, 2014): 1210–11. doi:10.1126/science.1249625

Wikipedia.org

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