Conventional Capacitors

Conventional capacitors are made up of two conducting electrodes which are further separated by an insulating dielectric material. Opposite charges build up on the surfaces of each electrode, when a voltage is applied on capacitor. The charges are separated by the dielectric, thus establishing an electric field that allows the capacitor to store energy. Capacitance C can be defined as: (1.1)

Where Q is stored charge and V is applied voltage. It should be noted that C is directly proportional to the surface area A of each electrode and inversely proportional to the distance D between the electrodes. (1.2)

Where ∈ is the dielectric constant.

Conventional capacitors have fairly high power densities, but quite low energy densities when compared to electrochemical batteries and to fuel cells. That is, a battery can store more energy than a capacitor, but it cannot deliver it very rapidly, which means its power density is low. On the other hand, capacitors can store relatively less energy per unit mass or volume, but whatever electrical energy they store, it can be discharged quickly to produce a lot of power, so supercapacitors are ruled by the same fundamental principles as conventional capacitors. However, they include electrodes with much higher surface areas A and much thinner dielectrics that reduce the distance D between the electrodes. Thus by Equation 1.2 and 1.3 , this results into increase in both capacitance and energy. Furthermore, by maintaining the low ESR characteristic of conventional capacitors, supercapacitors are able to attain comparable power densities also. Low ESR means low equivalent series resistance which is inversely proportional to power