Ultracapacitors Beyond EEStor

EEStor grabs all the attention on ultracapacitors, but EEStor is far from the only ultracapacitors story. Capacitors are electrical storage devices that should not be confused with batteries. In a battery, the electrical charge is stored chemically, in capacitors the charge is stored on the surface of some substance. When a battery is charged, chemical changes occur in substances or inside the battery. When a battery is discharged the substances change back to their original state. In most capacitor, electrons flow between two plates made of metal or other materials so positive and negative charges build up on the surface of the plates. The human body can itself act like a capacitor. Anyone who has been shocked while getting out of a car, or after walking over a rug, has experienced the consequence of having an electrical charge build up on his or her body. The shock comes when the built up electrical charge is rapidly discharged into some grounded source.

Since the classic capacitor involves the transfer of electrons from one substance to another, capacitors are limited in the amount of charge they can hold without a discharge. Without insulators called dielectric spacers, there will be a spark between the two plates.

Ultracapacitors use some material that increases the surface area on which electrons can be stored. Materials with lots of tiny holes in them called "nanoporous material" can be useful in ultracapacitor construction. Electrons find homes in all the little holes, and there accumulation builds up the charge of the ultracapacitor. Activated charcoal is one such material although researchers point to its limitations. Carbon-nanotubes developed by MIT potentially can hold larger charges. EEStor uses a substance called barium titanate, and claims that that its barium titanate technology can store about 8 times as much electricity per unit of weight as led acid batteries can. Barium titanate ultra capacitors, according to EEStor, can store up to 2 1/2 times the amount of electricity that a lithium-ion battery can. Carbon-nanotubes capacitors, in contrast, can theoretically hold about half of the charge of a lithium-ion battery per a given unit of weight.

Ultracapacitors can be charged and discharged much more rapidly than batteries.

Ultracapacitors do age, but probably can be expected to age more slowly than batteries. I do not recall seeing any EEStor estimates on how many charge-discharge cycles can be expected with an EESU.

A failure of the EEStor project would not be the end of the usefulness of ultracapacitors for transportation. Ultracapacitors would be useful as a source of energy for urban trucking, urban buses and light rail systems, and the electrification of national rail systems. China, beset by extreme air pollution problems, is already experimenting with ultracapacitor powered buses. Ultracapacitors that have the electrical storage capacity of carbon-nanotube, could make an electrified transportation system work. Such ultracapacitors have fewer limitations than lithium-ion batteries, even though carbon-nanotube ultracapacitors will weigh twice as much per unit electrical storage. Thus it is very like that even without a successful EEStor product, ultracapacitors are destined to play a major role in the electrification of transportation and indeed the electrification of society.

In addition to developments in ultracapacitor technology, a recent break through in lithium-ion battery technology has the potential of dramatically improving that technology. Dr. Yi Cui of stanford University has recently announced that the use silicon nanowires in ithium-ion batteries would increase their storage capacity by several fold, while greatly improving battery life. Dr Yi expects at least 1000 charge recharge cycles with his new battery technology.