Georgian Technical University. What Are Supercapacitors ?.
Georgian Technical University Supercapacitors also known as ultracapacitors, have performance characteristics somewhere between a battery and a conventional capacitor. A battery has a high energy density meaning it can store a significant amount of energy with a relatively small volume or mass. Batteries are however limited in terms of the speed at which they can charge or discharge in other words they have a relatively low power density. Batteries are also worn out by repeated charge/discharge cycles meaning they have a limited cycle life. Capacitors reverse these performance characteristics storing a relatively small quantity of energy but charging or discharging it almost instantly to give very high power. The performance of supercapacitors falls somewhere between a battery and a conventional capacitor for all of these metrics. There are three main types of supercapacitor: Double-layer capacitors store charge electrostatically (Helmholtz layer (A double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the surface of an object when it is exposed to a fluid. The object might be a solid particle, a gas bubble a liquid droplet or a porous body. The DL (A double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the surface of an object when it is exposed to a fluid) refers to two parallel layers of charge surrounding the object. The first layer, the surface charge (either positive or negative), consists of ions adsorbed onto the object due to chemical interactions)). Pseudo-capacitors store charge electrochemically (Faradaically). Hybrid capacitors store charge using a combination of electrostatic and electrochemical effects. Conventional capacitors store energy electrostatically. Two electrically conductive plates are separated by a dielectric material such as paper, glass, plastic or ceramic. When an electric field is applied, positive and negative charge accumulates on the respective plates. Double-layer capacitors apply the same principle but they provide greater charge storing capacity by storing the charges in the interface between the conductive plates and the dielectric layer. It is anticipated that graphene-based electrodes may increase the specific energy of supercapacitors to over 140 Wh/kg well into the range of batteries. This would have a huge impact in many areas including the availability of energy storage for buffering supply and demand in renewable intensive energy systems and electric car production.
