Electrochemical capacitor belongs to super capacitor(also called as ultracapacitor, Electrical Double-Layer Capacitor, gold capacitor and farad capacitor), which is a new energy storage device between capacitor and battery. Compared with traditional capacitors, electrochemical capacitors have higher specific capacity. Compared with the battery, it has the advantages of higher specific power, instant release of large current, short charging time, high charging efficiency, long cycle life, no memory effect and maintenance free. Therefore, it has great potential application value in mobile communication, consumer electronics, electric vehicles, aerospace and other fields.

The unit of the electrochemical capacitor is composed of a pair of electrodes, diaphragms and electrolytes. Between the two electrodes is a diaphragm with electron blocking and ion conduction. Both the diaphragm and the electrode are immersed in electrolyte. Carbon materials, metal oxides and conducting polymers are the main electrode materials for electrochemical capacitors. Carbon based materials are the most suitable electrode materials for supercapacitors in industrialization at present. Recent studies focus on improving the specific surface area and controlling the pore size and pore size distribution of the materials.

At present, materials based on carbon include activated carbon powder, activated carbon fiber, carbon aerogel, carbon nanotubes, nano carbon fiber and so on. Carbon based materials have stable performance and low price, but the electrode internal resistance is large, so it is not suitable to work under high current. Metal oxides are mainly focused on ruthenium dioxide (RuO2). Its conductivity is two orders of magnitude larger than that of materials based on carbon, and it is stable in sulfuric acid solution with a specific capacitance of 768 F/g. It is an ideal metal oxide electrode material at present, but its price is high. Therefore, it is a hot spot to find a kind of electrode material with stable performance and low price.

Compared with batteries and traditional physical capacitors, electrochemical capacitors have the following advantages:

1. High power density.
It can reach 102~104 W/kg, which is much higher than the power density level of battery.

2. Long cycle life.
After a few seconds of high-speed deep charge and discharge cycles of 500,000 to 1,000,000 times, the characteristics of supercapacitors change little, and the capacity and internal resistance only decrease by 10% ~ 20%.