Technologies

Graphene-based supercapacitors are said to store almost as much energy as lithium-ion batteries, charge and discharge in seconds and maintain all this over tens of thousands of charging cycles. One of the ways to achieve this is by using a highly porous form of graphene with a large internal surface area (made by packing graphene powder into a coin-shaped cell and then drying and pressing it).

Graphene is a thin layer of pure carbon, tightly packed and bonded in a hexagonal honeycomb lattice. It is widely regarded as a "wonder material" because it is endowed with an abundance of great traits: it is the thinnest compound known to man at one atom thick and the best-known conductor. It also has impressive strength and light absorption traits and is even considered ecologically friendly and sustainable as carbon is widespread in nature and part of the human body.

Graphene is often suggested as a replacement for activated carbon in supercapacitors, partly due to its high relative surface area (which is even more substantial than that of activated carbon). The surface area is one of the limitations of capacitance, and a higher surface area means better electrostatic charge storage. In addition, graphene-based supercapacitors will utilize their lightweight nature, elastic properties and mechanical strength.

Ultracapacitors, also known as EDLC (electric double-layer capacitors), differ from regular capacitors because they can store tremendous amounts of energy.

A primary capacitor usually consists of two metal plates separated by an insulator (like air or a plastic film). During charging, electrons accumulate on one conductor and depart from the other. One side gains a negative charge while the other builds a positive one. The insulator disturbs the natural pull of the negative charge towards the positive one, and that tension creates an electric field. Once electrons are given a path to the other side, discharge occurs.

Supercapacitors also contain two metal plates, only coated with a porous material known as activated carbon. They are immersed in an electrolyte of positive and negative ions dissolved in a solvent. One plate is positive, and the other is negative. During charging, ions from the electrolyte accumulate on the surface of each carbon-coated plate. Supercapacitors also store energy in an electric field that is formed between two oppositely charged particles, only they have the electrolyte in which an equal number of positive and negative ions is uniformly dispersed. Thus, during charging, each electrode has two layers of charge coating (electric double-layer).

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