Ultracapacitors - Review of Literature

Ever wonder about electric cars? Even in this 21st century, with many technological advances, electric cars are still not commercially viable. Batteries, the main source of energy storage for running electric cars, have many disadvantages. Is there a solution to this problem? The capacitor, an alternative energy storage device is competing to replace the battery in many electrical appliances, including the electric car. At the moment, batteries have higher energy densities than capacitors. However, capacitors posses something that batteries can never have, and it is the ability to give quick high voltage bursts when needed. This is essential for the acceleration and speed of the car. Thanks to nano-technology and surface chemistry, recent breakthroughs in the field of capacitors, has brought about the new breed of capacitors, called ultracapacitors. Scientists expect that future capacitors can be charged for five minutes and run a car for up to 500 miles (CNN, 2007, p.1). This could greatly affect the future in the way the world powers objects. Say good-bye to batteries because capacitors are going to change the way mankind thinks about energy resources. Electric cars will run much better on capacitors rather than batteries because capacitors can be powered faster, providing a better start up and acceleration for the car, and are considerably lighter, and will last longer. The battle between batteries and capacitors is on.

Electricity, the subject of this project, is the most efficient and widely used energy source in this industrialized world. Electricity consists of charged particles that have either a positive or a negative charge. There are two basic types of electricity: static electricity, and electric current. Rubbing two dissimilar materials together creates static electricity (Static Electricity, 2006, para. 8). Lightning is a good example of static electricity, which occurs during the discharge between parts of positive and negative charge caused by atmospheric convection. Static electricity also remains stationary until used to power some electrical appliance. The Greeks were the first to test static electricity by rubbing amber, a reddish orange stone, with fur or wool, and discovered that it created magnetism to some extent. This is because of the difference in the ionization energy in the two objects. When two objects rub together, the electrons in the object with the lesser ionization energy give up an electron to one with the higher ionization energy. Static electricity also creates polarity because of the greater number of positive or negative electrons in one object. Static electricity is used in capacitors to store energy, which enables it to release energy whenever needed. In contrast, the electric current is always in motion and can easily flow through conductors. Electric current is the flow of charged particles in a particular direction. It is the primary source of energy for domestic and industrial sectors. Whether it is static or current, the storage of electricity is a difficult preposition.

The study of capacitors and other electrical devices involve many fundamental electrical quantities and units. Voltage, current, and time are the dependent variables. Voltage, probably the most commonly used electrical term, refers to the electric pressure or electromotive force that creates current flow. The formula for Voltage (V) is Energy (W) over Charge (Q) (V = W/Q) (Flower, 2003, p.23). Energy is the ability to do work and is measured in Joules. The unit of electrical charge is the coulomb, which is equal to the charge of 6.25 x 1018 electrons. High power output is one of the main advantages capacitors have over batteries. Power is the rate at which energy is delivered. The formula for Power (P) is Energy (W) over Time (T). Power is measured in joules per second. The next primary measure in electrical science is the current. Current is the amount of charge and time it takes to move past a certain point. Current is measured in amperes; one ampere is one coulomb per second in a circuit. Electric current refers to current in a specific direction. Resistance slows down current, and is measured in Ohm’s. Ohm’s law founded by Georg Simon Ohm relates current, resistance, and voltage, (potential difference) in a circuit. “Ohm’s law states that the potential difference is the product of the current and resistance in a circuit so that the current is inversely proportional to the resistance for a given voltage” (How it Works Science and Technology, 2003, p.726). The mathematical equation that explains this law is Resistance (R) = Voltage (V)/Current (I). Resistivity is the resistance of a cubic size of an object. Resistivity = Resistance * area / length. This equation can be reversed to figure out the current and voltage, which makes it a very useful tool. Another important law, Coulomb’s law, founded by Coulomb and Priestly, states that the force between two charged objects varies inversely with the reciprocal of the square of the distance between them (How it Work Science and Technology, 2003, p.726). All of the above stated fundamental electrical units are integral to the functioning of the capacitor.