Research on Classification and Characteristics of Supercapacitors

Supercapacitor is a new type of energy storage device with high power density, short charging time, long cycle life, and environmental protection. It can be applied to energy storage devices, power supply systems and many electronic devices. As a new type of green energy storage device, supercapacitor has shown great application potential or prospect in many industries or fields.

What is a supercapacitor

Supercapacitor, also known as electrochemical capacitor, is a new type of energy storage device that relies mainly on electric double layer and redox tantalum capacitor to store electrical energy. Unlike traditional chemical power supplies, supercapacitors are a power source between a conventional capacitor and a battery. They have the advantages of high power density, short charge and discharge time, long cycle life, and wide operating temperature range.

Classification of supercapacitors

Supercapacitors can be divided into two categories according to their energy storage principles: electric double layer capacitors and pseudocapacitor (Faraday tantalum capacitors).

(1) Electric double layer capacitor

An electrochemical double layer capacitor (EDLC) is a device that uses an interface electric double layer capacitor formed between an electrode and an electrolyte to store energy. The energy storage mechanism is an electric double layer theory. The electric double layer theory was first proposed by the German physicist Helmhotz at the end of the 19th century. Later, it was modified and improved by Gouy, Chapma and Stern according to the influence of particle thermal motion, and gradually formed a complete theory for electric double layer capacitors, and laid the theoretical foundation. The electric double layer theory holds that when the electrode is inserted into the electrolyte, the net charge on the surface of the electrode will attract some of the irregularly distributed ions with different charges from the solution, so that they are separated from the electrode on the solution side of the electrode-solution interface. The distance is arranged to form an interface layer having the same number of charges as the remaining charge on the electrode surface and having opposite signs.

Distribution of Electric double layer capacitor

An electric double layer capacitor is a process in which charge and discharge are performed by using an electric double layer mechanism. The positive and negative ions of the electrolyte accumulate at the interface double layer of the electrode material/electrolyte during charging to compensate for the electrons on the surface of the electrode. In particular, when charging is forced to form an ion double layer, more oppositely charged ions accumulate in the bilayer of the positive and negative interfaces, and a relatively high electric field is generated, thereby realizing energy storage. During discharge, as the potential difference between the two plates decreases, the positive and negative ion charges return to the electrolyte, and the electrons flow into the load of the external circuit, thereby realizing the release of energy.

(2) Faraday pseudocapacitor

On a two-dimensional or quasi-two-dimensional space in the surface or bulk of the electrode, the electrode active material is subjected to underpotential deposition, and a highly reversible chemisorption desorption or redox reaction occurs, generating a capacitance related to the charge potential of the electrode. Faraday's pseudocapacitor can store charge in two ways: one is to store the charge through storage on the electric double layer; the other is through the rapid reversible redox reaction of the ions in the electrolyte in the electrode active material. Although the electron transfer of the Faraday pseudocapacitor is generated, it is highly dynamic reversible unlike the charge and discharge behavior of the battery, and is closer to the characteristics of the capacitor.

Characteristics of Supercapacitor

At present, supercapacitors have formed a series of products, achieving a capacitance of 0.5 to 1000 F, a worker voltage of 12 to 400 V, and a maximum discharge current of 400 to 2000 A. Compared with batteries, supercapacitors have the following performance characteristics:

(1) Large capacitance with a Farad class;

(2) The pulse power is nearly 10 times higher than the battery;

(3) The charge and discharge cycle life is more than 100 000 times;

(4) It can be used normally in the ambient temperature of -40°C~70°C;

(5) It has a strong charge retention capability and the leakage power is very small;

(6) Fast charging and convenient use;

(7) No pollution, truly maintenance free.

Edited by Suzhou Yacoo Science Co., Ltd.