Super-capacitors Vs. Capacitors  No conventional dielectric  Two layers of the same substrate, result in the effective separation of charge  Lack of dielectric results in a packing of layers which result in higher surface area  Capacitance can reach Thousands of Farads  Two parallel plates with dielectric  Limited surface area, limiting capacitance

Double Layer Capacitor  have double layer construction consisting of two carbon electrodes immersed in an organic electrolyte  During charging, the electrically charged ions in the electrolyte migrate towards the electrodes of opposite polarity  No chemical action equals typical cycle life in hundreds of thousands

Activated Carbon Vs Carbon Nanotube Carbon NanotubeActivated Carbon(or activated charcoal)

 Activated Carbon: is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reaction.  powder made up of extremely small and very "rough" particles, which in bulk form a low-density volume of particles with holes between them that resembles a sponge.  The overall surface area allow many more electrons to be stored in any given volume than other conductors such as aluminum.  The downside is that the charcoal takes the place of the improved insulators used in conventional devices, so in general electric double-layer capacitors use low potentials on the order of 2 to 3 V.

 Experimental devices developed at MIT replace the charcoal with carbon nanotubes, which have similar charge storage capability as charcoal (which is almost pure carbon) but are mechanically arranged in a much more regular pattern that exposes a much greater suitable surface area.  By using vertically aligned, single-wall carbon nanotubes which are only several atomic diameters in width instead of the porous, amorphous carbon normally employed, the effective area of the electrodes (plates) can be dramatically increased.  This still won’t achieve the levels of energy of a rechargeable battery, but it will increase the power density

AdvantagesDisadvantages  High power available.  High power density.  No special charging or voltage detection circuits required.  Can be charged and discharged in seconds.  Can not be overcharged.  Long cycle life of more than 500,000 cycles.  No chemical actions.  10 to12 year life  Low impedance  Linear discharge voltage characteristic prevents use of all the available energy in some applications.  Power only available for a very short duration.  Low capacity.  Low energy density. (6Wh/Kg)  High self discharge rate. Much higher than batteries.  Upper and lower voltage is limited to main energy source (battery), leading to wasted energy.

Batteries Vs. Super-Capacitors  Super-capacitors can have power densities that are 100 times greater than that of batteries  Power density combines the energy density with the speed that the energy can be drawn out of the device  Batteries have relatively slow charge and discharge times.  Super capacitors offer a more environmentally friendly option than batteries because of their long lifespan.  However batteries store more energy than super-capacitors

Applications  Super-capacitors are used to provide fast acting short term power back up for uninterruptable power supply(UPS) applications.  Battery life can be extended, with battery super-capacitor combinations.  The batteries provide average power and super- capacitors provide short duration peak power boost, reducing the peak loads on the battery and permitting the use of smaller batteries.

Hybrid Electric Vehicles  The CSIRO in australia [national science agency] has developed the UltraBattery, which combines a supercapacitor and a lead acid battery in a single unit  4x longer life cycle, 50% more power, 70% cheaper than batteries used in HEV’s