Supercapacitor - manufacturing, applications and future trends

At present, energy storage systems play an increasingly important role in different fields, such as electric vehicles, power systems and other typical fields. In this context, as an energy storage technology, supercapacitor has become a hot topic in academia and industry due to their excellent properties such as high power density, maintenance-free, and long life.

This paper analyzes the research status and application of supercapacitor, and forecasts and analyzes the future development trend of supercapacitor according to market applications.

1. Introduction to supercapacitor

Compared with traditional electrochemical energy storage technology,such as flywheel energy storage,  supercapacitor has the advantages of high output power, fast response, maintenance free, long life, wide operating temperature and so on, which can meet the requirements of many fields. At present, the market size and application fields are growing.

In recent years, supercapacitor technology has progressed rapidly, especially in academia, where new technological breakthroughs have been reported. With the support of academia, the industry has also made great progress in manufacturing and application.

2. Manufacturing of supercapacitor

Supercapacitor is mainly composed of electrodes, electrolytes, separators, current collectors and other parts. The main function of the electrode is to store energy, the main function of the diaphragm is to prevent the short circuit of electrons inside the capacitor, and the current collector is used to collect current and carry the electrode active material. For supercapacitor, the adhesion thickness of the electrode active material on the surface of the current collector and related processes will greatly affect the performance of the supercapacitor, which is the key to the fabrication of the capacitor.

Most of the commercial supercapacitor is cylindrical in shape, which is mainly composed of two electrodes attached to an aluminum current collector active material. The separator is located between the two electrodes to prevent the formation of an electronic short circuit, and the cathode and anode output ends are respectively located at the upper and lower ends of the winding core winding. When the winding is completed, the fabricated core winding is placed in a hard shell, the cathode and anode output ends are connected to the shell, and electrolyte is injected for sealing to prevent impurities from polluting the electrolyte and active materials.

Maxwell, as the world's top supplier of supercapacitor, has the most advanced manufacturing technology of supercapacitor. Maxwell is one of the few manufacturers in the world that has mastered the dry manufacturing technology of supercapacitor electrodes. Based on this technology, it was acquired by Tesla, a well-known electric vehicle supplier, in the first half of 2019. After years of development, the cylindrical capacitor diameter of the company has been standardized, the product diameter is 60mm, by adjusting the height of the product, to meet the requirements of different capacity.

Cylindrical supercapacitor have a high level of production automation and low manufacturing costs, which can meet applications in different fields. The main disadvantage of this type of supercapacitor is that the heat dissipation performance is poor. When the capacitor is charged and discharged with high power, a large amount of heat is rapidly generated inside, which cannot be dissipated through the thick electrode layer in time. Despite the high efficiency and low power loss ratio of supercapacitor, temperature is still an important factor limiting products to achieve ultra-high power charge and discharge.

In order to improve the heat dissipation performance of the product, Ioxs has designed another type of supercapacitor, which is a flexible packaged supercapacitor. The production process of the product is similar to that of the flexible packaging lithium-ion battery. It is produced by a lamination process. The electrodes with the same polarity are stacked and connected in parallel, and the product is sealed by an aluminum-plastic film. The price of this type of product is higher than the price of cylindrical products, because of its excellent heat dissipation performance, it is suitable for ultra-high power application scenarios.

At present, cost reduction is a hot direction in the development of supercapacitor, mainly through the development of low-cost materials and research on new low-cost production processes to reduce product costs. Some studies suggest that when the cost of materials drops by 90%, the price of supercapacitor products will drop by 50%. At present, some new production processes are in the research stage. It is expected that in the next few years, there will be a major breakthrough in the production process of supercapacitor, and then the product price will further decline.

Compared with other electrochemical energy storage technologies, especially compared with lithium ion battery storage and lead-acid battery, supercapacitor exhibit a wider operating temperature range. Among them, the operating temperature range of hybrid electrode supercapacitor is -25°C-60°C. Although it is a type of supercapacitor with the narrowest operating temperature range, it also exceeds the operating temperature range of traditional lithium-ion batteries and lead-acid batteries.

3. Application of supercapacitor

① Applications in transportation

The application of supercapacitor in the field of rail transit is relatively mature. It can realize regenerative braking of electric traction, stabilize the voltage of the overhead contact network, save power energy and ensure the stable power supply of the power system.

City buses are another important market for supercapacitor. The operating conditions of buses, which frequently start and stop, are very suitable for supercapacitor. The application of supercapacitor in this field is mainly through the combination with battery energy storage system or the supercapacitor as an independent energy storage system. The stored energy can maintain the car and the car running to the next station and charging at the next station.

In addition to rail systems and public transport, the use of supercapacitor in commercial vehicles (fuel cells, hybrids, pure electric) is also on the rise. At present, the aerospace industry is developing towards electrification, and more and more electrical devices are proposed for use in the aerospace field, such as aircraft emergency power supplies. Supercapacitor can be combined with ESS energy storage systems as high-power energy storage devices to build hybrid ESS energy storage systems to meet the high power requirements of equipment.

② Energy field

Supercapacitor has the characteristics of maintenance-free, long life, high power, and the ability to meet extreme climate requirements. Supercapacitor is attractive to related fields such as renewable energy. The main use of supercapacitor in renewable energy systems is for pitch control of wind turbines. Data shows that 20%-30% of wind power generation is equipped with supercapacitor pitch control system, and 30%-45% of wind turbines are equipped with battery energy storage system.

Microgrids are usually equipped with renewable energy generators, and the grid connection of microgrids is currently subject to certain restrictions to avoid reducing the interference caused by microgrids to the grid. Therefore, it is of great significance to choose a suitable ESS and its management strategy. Supercapacitor has some defects in improving battery energy storage systems and improve the performance of battery discharge power, and can be used in microgrids in conjunction with battery energy storage systems.

In addition, supercapacitor can be used in standalone microgrids to provide services such as high resilience and fast response. Supercapacitor helps the system meet its power needs at frequencies of a few Hertz. The system has higher efficiency and prolongs the service life of the fuel battery.

In addition, in 2013, the Spanish microgrid was also equipped with a supercapacitor energy storage system, with a maximum discharge of 4MW and a capacity of 5.5KWh; The 23 cranes in Shanghai Port have a great impact on the power grid. In order to reduce the impact of the cranes on the power grid, a 3MW/17.2KWh supercapacitor energy storage system is installed as a backup source, which can continuously provide power supply for 20s.

③ Industrial field

In industry, supercapacitors can be used in forklifts, forklifts, agricultural machinery, mining shovels, port cranes and industrial lasers. Among these facilities, forklifts have seen the fastest growth. Forklift trucks generally use battery energy storage systems or fuel cell systems to power them. Supercapacitor energy storage systems can serve as auxiliary power supply systems, support the system to achieve high power discharge, and recover relevant energy during braking.

In port cranes, cranes equipped with supercapacitor can recover energy from braking and descent operations, which can save about 20% of fuel. At the same time, supercapacitor can provide large discharge power, which can assist the engine and greatly reduce the engine power. As a large mechanical equipment, excavator needs higher output power. The combination of super capacitor and diesel engine can support the equipment to provide higher output power.

④ Electronic products field

Consumer electronics are particularly sensitive from supercapacitor to the volume of supercapacitor products. The market of consumer electronics products is diversified. In summary, the use of supercapacitor in these products can be mainly divided into four categories:

• The backup power is stored in the memory in a timely manner, mainly used in the solid-state hard disk;
• Backup the power supply after the main power supply is faulty;
• Supercapacitor replaces batteries as an energy storage system, typically including flashlight power supply and solar energy collection system;
• In 2013, STMicroelectronics launched the integrated camera control system using supercapacitor.

4. Development trend of supercapacitor

According to the market application analysis of supercapacitor, the current supercapacitor is limited by low energy density and are mainly used as auxiliary power sources, but are rarely used as main power sources. In order to achieve a major breakthrough in the application field of supercapacitor market, it depends on the continuous breakthrough of supercapacitor technology in the future. The development trend of supercapacitor is as follows:

● Low cost, high energy density, the future supercapacitor as the main power source of equipment or system, high energy density and low cost is the only way;

● Ultra-high power density, low maintenance cost, and long service life. The development of supercapacitor to higher power density, maintenance-free and long-life will make up for the low energy density of products to a certain extent, and can further expand the market share in some special fields, and organic system supercapacitors is expected to take the lead in achieving ultra-high power breakthrough;

● The research on the aging mechanism of supercapacitor and the control strategy of supercapacitor energy storage system will be another research hotspot of supercapacitor, which will help to optimize the design of supercapacitor energy storage system and minimize the adverse factors caused by the design of the system.

If there is a big breakthrough in the above technologies, supercapacitor will have greater advantages in power density, maintenance cost, service life and environmental adaptability compared with battery energy storage, and will become an ideal choice for energy storage systems in electrical, electric power, electronics and other industries.

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