Supercapacitors, also known as electric double-layer capacitors and electrochemical capacitors, are a new type of electrochemical energy storage device with electrochemical performance between traditional capacitors and batteries. It mainly stores energy through the electric double layer capacitance and the Faraday quasi-capacitor produced by the redox reaction. Generally speaking, the energy storage mode of supercapacitors is reversible, so it can be used to solve problems such as battery memory. Currently, the application range of super capacitors is very wide, especially in hybrid vehicles. As the power source of hybrid electric vehicles, it can well meet the high-power requirements of the vehicle when starting, climbing and accelerating, thereby effectively saving energy and increasing battery life. 

For super capacitors, there can be different classification methods based on different contents. First, according to different energy storage mechanisms, supercapacitors can be divided into two categories: electric double layer capacitors and Faraday quasi-capacitors. Among them, the electric double-layer capacitor mainly generates stored energy through the adsorption of pure electrostatic charges on the electrode surface. Faraday quasi-capacitors mainly generate Faraday quasi-capacitors through Faraday quasi-capacitance active electrode materials (such as transition metal oxides and polymer) surface and near the surface of reversible redox reactions to generate Faraday quasi-capacitors, thereby achieving energy storage and conversion. Secondly, according to the type of electrolyte, it can be divided into two categories: water-based supercapacitors and organic supercapacitors. In addition, according to whether the types of active materials are the same, they can be divided into symmetric supercapacitors and asymmetric supercapacitors. Finally, according to the state and form of the electrolyte, supercapacitors can be divided into solid electrolyte supercapacitors and liquid electrolyte supercapacitors.