Supercapacitors

as Energy Storage Devices

Capacitance

● A measure of ability to store electric charge o Ratio of magnitude of charge on either

conductor to potential difference/voltage between conductors

Capacitance

Charge on either conductor

Potential difference

What is a capacitor?

Dielectric, K

Remember Physics 153?

Energy Storage in Capacitor

The more work you can put into the capacitor…

That essentially becomes the energy the capacitor stores.

Wait, what are dielectrics?

To refresh your memory:● Store more energy than usual

o Polarization of dielectric moleculeso Charge separation between plates

● However, they put a limit on how much voltage can be applied

Dielectric Breakdown

Dielectrics prevent current from flowing between electrodes.It basically acts as an insulator.

But if you apply too much voltage… It conducts!

How can we increase the amount of charge stored if we can’t apply too much voltage?

Optimal Capacitor

Easiest way to increase capacitance (hence, energy storage):● Increase surface area● Decrease plate separation

This is exactly what a supercapacitor does.

Also known as...

● Electric Double Layer Capacitor (EDLC)

● Electrochemical Double Layer

Capacitor

● Double Layer Capacitor

Supercapacitor

Battery

Battery vs. Supercapacitor• The cycle life of battery cells is restricted

to one thousand discharge/recharge

cycles

• Electron transfer occurs across the two

electrodes with the electrolyte as the

medium transfer

• The charge storage by REDOX reaction

occurs in the battery

• Lower power density

● 100 times shorter than the conventional electrochemical cell

● REDOX reaction across the double layers

● In the form of Helmholtz capacitance and space-charge capacitance

● Higher power density

● Functions over a larger range of temperature

Battery vs. Supercapacitor

Capacitance

Helmholtz Layer Capacitance

(Electrochemical)

• The charge transfer process at the electrode

depends on the work function, φ of the metal electrode.

• Gs ≈ ½ (CV2)

the change in the Gibbs free energy of

ion solvation

• Their behaviour depends on the dipole moment that controls the current density and dielectric constant

Space Charge Capacitance

(Electrostatic)

• Large area of porous carbon electrodes facilitates the adsorptions of the solvation ions from the electrolyte

• E (electric field) = ∆V/D and the space charge capacitance value is determined by C = ( A)/D∈

• It is measured that the double layer’s field strength is about 5000kV/mm

Method of Processing

●Efficient

●Less time consumption

●Uses inexpensive materials

■LightScribe DVD burner

■DVD disc

■Graphite Oxide

●Can manufacture into different size for various purposes

●Easily integrated to modern electrical devices

●Adjustable thickness of graphene

Method of Processing1. A layer of plastic is attached on

the surface of a DVD disk

2. Graphite Oxide is then coated on the plastic

3. Laser in the LightScribe DVD optical drive will etch the on the surface of the graphite oxide

4. The graphite oxide will turn into graphene once it has been etched by the laser

5. The pattern on the graphene has been already designed into different structure for various purpose

Applications of Supercapacitors

●Reduced size and weight but without reducing performance and durability

●Fully integrated with smaller and lightweight systems

●Consumer, industry, military, medical and transportation use

○Laser power supply

○Medical pacemaker

■Energy pulse released is able to charge up a pacemaker to 500 Joules

Marketing and Commercial Logistics

●Large multinational firms (Maxwell Technologies Inc.)○Target the electronics industry

●Dedicated capacitor firms ○Large energy storage applications

●Early stages of commercialization

●Began to move into more mainstream applications

●Transitioning from an emerging phase to a growth phase

●Hybrid electric vehicle and renewable energy markets

Benefits and Limitations

● Virtually unlimited cycle life

○ Can be cycled millions of time

● High specific power

○ Low resistance to high load

currents

● Excellence on low temperature

charge and discharge performance

● Cost effective energy storage

● Charges in seconds

○ No end-of-charge termination

required

● Can be easily disposed because it is

made out of carbon

● Low specific energy

○ Holds a fraction of a regular

battery

● Linear discharge prevents using

the full energy spectrum

● High self-discharge

○ Higher than most batteries

● low cell voltage

● High cost per watts

Conclusion

Recently, Dr. Richard Kaner and his team at UCLA created supercapacitor with energy density comparable to batteries

Lightweight, flexible electronics… even electric vehicles!