Basic Principles of Supercapacitors

                           Basic principles of supercapacitors

Supercapacitors, also known as electrochemical double-layer capacitors or supercapacitors, have emerged in the field of energy storage due to their excellent performance characteristics. Compared with traditional capacitors, supercapacitors can store more energy and have the ability to charge and discharge quickly. This article will comprehensively analyze the working principle, key technologies, typical applications and future development trends of supercapacitors.

1. Basic principles of supercapacitors

The energy storage mechanism of supercapacitors mainly relies on the electrochemical double layer effect and the Faraday quasi-pseudocapacitance effect.

1. Electrochemical double layer effect

When the electrodes of a supercapacitor are immersed in an electrolyte solution, a layer of ions with opposite charges is adsorbed on the electrode surface to form the so-called electrochemical double layer. The electric field between this ion layer and the electrode surface can store charge, similar to the electric field in a traditional capacitor.

2. Faraday quasi-pseudocapacitance effect

In addition to the electrochemical double layer effect, supercapacitors can also store energy through the Faraday quasi-pseudocapacitance effect. When current passes through the electrode material, a surface redox reaction occurs, causing the charge to be stored inside the electrode material, thereby increasing the total capacity of the capacitor.

2. Key technologies of supercapacitors

The performance of supercapacitors depends on the design and selection of their electrode materials, electrolytes, diaphragms and current collectors.

1. Electrode materials

Activated carbon: has a high specific surface area and can provide a large electrochemically active surface area.

Carbon nanotubes (CNTs): have high mechanical strength and conductivity.

Graphene: has an ultra-high specific surface area and excellent conductivity.

Metal oxides and hydroxides: such as RuO₂, Ni(OH)₂, etc., store charge through surface redox reactions.

2. Electrolyte

Aqueous electrolytes: such as sulfuric acid and phosphoric acid, which are low in cost and safe.

Organic electrolytes: such as acetone and acetonitrile, which can provide higher operating voltages.

3. Diaphragm

The function of the diaphragm is to prevent the two electrodes from directly contacting each other and causing a short circuit, while allowing ions to pass through. Commonly used diaphragm materials include polyethylene (PE), polypropylene (PP), etc.

4. Current collector

The current collector is used to conduct current and fix the electrode material inside the capacitor. Commonly used current collector materials include aluminum foil, stainless steel, etc.

3. Application Cases of Supercapacitors

Supercapacitors have found wide applications in many fields due to their unique performance characteristics.

1. Transportation

In hybrid electric vehicles (HEV) and electric buses (EV), supercapacitors can be used as auxiliary power or main power to provide instantaneous high power output to make up for the problem that the battery cannot provide enough energy in a short time. For example, in the startup phase of a bus, supercapacitors can quickly release energy to help the vehicle start smoothly.

2. Industrial Equipment

In industrial equipment, supercapacitors can be used in energy recovery systems, such as in elevators, cranes and other equipment. When the equipment is going down, supercapacitors can absorb the regenerated energy and release it when the equipment is going up, thereby saving energy.

3. Power System

Supercapacitors can be used for peak-shaving and valley-filling of power grids, by storing excess electrical energy during low-load periods and releasing it during peak load periods to balance the load of the power grid. In addition, in uninterruptible power supply (UPS) systems, supercapacitors can provide instantaneous high current support to ensure that the equipment can operate normally when the city power is interrupted.

4. Consumer electronics

In consumer electronics, supercapacitors can be used as backup power or main power to provide additional energy support for portable devices. For example, in digital cameras, supercapacitors can provide enough energy to drive the shutter at the moment of shooting.

IV. Development trend of supercapacitors

With the advancement of science and technology, supercapacitors are moving towards higher performance and wider application.

1. Research on new materials

Scientists are exploring new electrode materials, such as transition metal sulfides and nitrides, to further improve the energy density and power density of supercapacitors.

2. Structural optimization

By optimizing the design of the internal structure of the capacitor, such as using a three-dimensional porous structure, the effective area of the electrode can be increased, thereby improving the energy storage capacity of the capacitor.

3. System integration

As supercapacitor technology matures, more attention will be paid to its integration with other energy storage technologies (such as lithium-ion batteries) in the future to form a complementary energy storage system to meet diverse needs.

4. Miniaturization and flexibility

With the development of portable electronic devices, higher requirements are placed on miniaturized, lightweight and flexible supercapacitors. Researchers are working on developing flexible supercapacitors for wearable devices.