Graphene flake electrodes for super capacitor
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Graphene Flake Electrodes for Super Capacitor. Meng Jiao. Introduction of Super Capacitor. The fast development of electronics require new energy storage devices. 1. Smaller, lighter 2. High efficiency 3. Environmental friendly 4. Longer life 5. L ower cost.

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Graphene Flake Electrodes for Super Capacitor

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Graphene flake electrodes for super capacitor

Graphene Flake Electrodes for Super Capacitor

Meng Jiao

5/5/2010


Introduction of super capacitor

Introduction of Super Capacitor

  • The fast development of electronics require new energy storage devices.

    1. Smaller, lighter

    2. High efficiency

    3. Environmental friendly

    4. Longer life

    5. Lower cost

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Possible solution super capacitor

Possible solution: Super capacitor

  • 1. High energy density (unit: Wh/kg)

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Continued

Continued

  • 2. Efficiency comparison (Recharge)

    Data citied from:

    1. http://en.wikipedia.org/wiki/Electric_car

    2. John W. Stevens and Garth P. Corey, John W. Stevens and Garth P. Corey,

    (http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf )

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Continued1

continued

  • 3. Fast recharge

  • Ather advantages:

    1. low coast

    2. Longer life

    3. Environmental friendly

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How it works

How it works

Structure Scheme:

Electrodes: Made from large surface area material such as active carbon.

Ionic liquid: electrolyte

Separator: Effective ion conductor.

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Electric double layer edl

Electric Double Layer (EDL)

  • A model proposed by Helmholtz

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How this model works

How This Model Works

Assume no chemical reaction happen at electrode surface, then no charge transfer.

Ions form a thin layer on electrode.

Separation between them is determined by the radius of ions and the solvation shells.

A video lecture about EDL: http://www.youtube.com/watch?v=2zhQM0IfTcI

(Picture and material quote from http://www.cartage.org.lb/en/themes/sciences/Chemistry/Electrochemis/Electrochemical/ElectricalDouble/ElectricalDouble.htm)

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Large capacitance

Large Capacitance

  • Capacitance:

    C

  • EDL provide a charge separation d in order of Å. As comparison the thinnest dielectric man can made is about 2 μm.

  • Then we need to do is choose electrode with large surface area

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The electrode currently in use

The Electrode Currently in Use

  • Active carbon

Surface area:

500 m2/gram

Data and pic quoted from Wikipedia.

http://en.wikipedia.org/wiki/Activated_carbon

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Graphene

Graphene

Surface area of Graphene:

Single layer:

2500 m2/gram

Double Lyaer:

1200 m2/gram

(calculation are based on bond length 0.14nm)

Picture quoted form wikipedia

http://en.wikipedia.org/wiki/Graphene

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Electrode

Electrode

  • The proposed electrode are achieved by two approaches with exactly the same idea.

    Maximize the Area.

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Approach 1

Approach 1

  • Mix CNT with chemically prepared graphene flakes.

    (details of this process can be found in the paper J. Am. Chem. Soc., 1958, 80 (6), p 1339)

  • The purpose of adding CNT is to build a electronic conducting network. The graphenesuspended in the electrolyte to maximize the electrode surface area. They can pick up charges only when they in touch with the CNT network.

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Approach 2

Approach 2

  • Graphenenanomesh + graphene flakes.

    Details about carbon nanomesh please see JingweiBai, et al. Graphenenanomesh, Nature Nanotech. 5, 190 (2010)

  • The electrodes are composed with layers of nanomashes, which allow the free flow of electrolyte. In between layers, graphene flakes present to provide separation between mesh layers and maximize the surface area.

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Reference

Reference

  • JingweiBai, et al. Graphenenanomesh, Nature Nanotech. 5, 190 (2010)

  • paper J. Am. Chem. Soc., 1958, 80 (6), p 1339

  • http://en.wikipedia.org/wiki/Graphene

  • http://en.wikipedia.org/wiki/Activated_carbon

  • http://www.cartage.org.lb/en/themes/sciences/Chemistry/Electrochemis/Electrochemical/ElectricalDouble/ElectricalDouble.htm

  • http://www.youtube.com/watch?v=2zhQM0IfTcI

  • John W. Stevens and Garth P. Corey, John W. Stevens and Garth P. Corey, http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf

  • http://en.wikipedia.org/wiki/Electric_double-layer_capacitor

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