supercapacitors as an energy storage device
TRANSCRIPT
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!