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Supercapacitor

Supercapacitor (SC)

To store the kinetic energy recovered it requires an electrical storage device with high power density rather than high energy density, as a brake sequence takes place in a short period of time and produces high power levels. The most common electrical energy storage unit today is the battery that stores energy electrochemically. Electrochemical storage means that chemical compounds are formed in the interface between cathode and electrolyte during discharge which give rise to released electrons. When the battery is then recharged, electrons are added, and the chemical process goes backwards. There are batteries in a variety of power densities but generally batteries have high energy density and low power density, which makes them highly inappropriate for a kinetic energy recovery system.

Supercapacitors and ultracapacitors are both just a different name for an electronic double layer capacitor (EDLC). Supercapacitors are a type of electrostatic energy storage which can store and release electrical energy through nanoscopic charge separation. Charge separation is fast and takes place at the interface between the porous electrode and an electrolyte. Paper-based supercapacitors have the potential for high capacitance, high cost efficiency, and to be completely environmentally friendly. Paper is an electrical insulator, but has high surface area and can easily be coated with an electrically conductive material to form a thin and cheap EDLC cell with high capacitance.

 

The figure shows a schematic sketch of a supercapacitor. Where (1) is the electrode material, (2) is a separator, (3) is the current collectors and (4) is the electrolyte.

 

Supercapacitors can store energy at high power levels with over 95% efficiency, giving a total KERS efficiency of about 80%.

We see a significant potential for development of SC. A contributing factor is the discovery of graphene for less than 10 years ago. The graphene can provide both excellent conductivity and very large surface. It can provide the SC with high capacitance and low internal resistance, which in turn can provide the SC with high specific power. This means that there is now possible to manufacture SC with properties that did not exist a few years ago.

 

The figure to the left shows a picture of graphene from a Transition Electron Microscope and the right figure shows paper coated with electrode material

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