Introduction to supercapacitors

Supercapacitors, also called ultracapacitors, electrochemical capacitors, electric double layer capacitors, gold capacitors or farad capacitors, are electrochemical devices developed from the 1970s and 1980s that store energy by polarising an electrolyte. Unlike conventional chemical power sources, they sit between conventional capacitors and batteries and have special characteristics. They store energy mainly through the electric double layer and through redox pseudo-capacitance. No chemical reaction takes place during storage, and the process is reversible, which is why a supercapacitor can be charged and discharged hundreds of thousands of times. As with other electric double layer capacitors, the basic principle is a double layer formed by a porous activated carbon electrode and an electrolyte, giving very large capacitance.

Types of supercapacitor

Supercapacitors are divided into electric double layer capacitors, pseudo-capacitors and hybrid supercapacitors. EDLCs offer high power density and long life but lower energy density, and are already commercialised. PCs offer higher energy density but are costly and technically immature. Hybrid supercapacitors offer high energy density and long life, are at an early stage of commercialisation and have broad prospects.

Electric double layer capacitors (EDLC). EDLCs store energy physically through the interface between a porous carbon electrode and the electrolyte. They operate between -40℃ and 70℃, have a cycle life of more than 1 million and are commercially available, making them the mainstream supercapacitor today. Based on pure electrostatic adsorption, they store energy in the double layer formed at the electrode and electrolyte interface, typically using high specific surface area materials such as activated carbon, carbon fibre or carbon aerogel as electrodes to maximise double layer capacitance. Because charging and discharging involve no chemical reaction, EDLCs have long cycle life and good temperature characteristics. Their advantages are high power density, long life and environmental friendliness, but energy density is relatively low.

Pseudo-capacitors (PCs). Also known as Faraday quasi-capacitors, PCs can be seen as a supplement to EDLCs, storing energy through reversible redox reactions on the surface of the electrode material. They typically use metal oxides such as MnO2, NiOx or V2O5, or conductive polymers such as PPy or PANI, as electrode material. Compared with EDLCs they provide higher energy density, operate between -20℃ and 65℃ and have a cycle life above 10,000. Current application costs are high, the technology is not yet mature and the industrialisation outlook is unclear.

Hybrid supercapacitors. Hybrid supercapacitors grew out of research on EDLCs and pseudo-capacitors. Their electrode materials include both activated carbon and secondary battery materials, combining physical and chemical storage. Energy density is relatively high and power density relatively low. They operate between -20℃ and 55℃, have a cycle life above 50,000 and are at an early commercial stage. They are an important direction for future supercapacitor research and have broad potential in electric vehicles, portable electronics and renewable energy storage.

Application areas of supercapacitors

In the power and energy sector, supercapacitors are used for grid frequency stability, smoothing the grid connection of wind and solar storage, and hybrid energy storage systems. In vehicles they serve as main power or safety redundant power, improving performance and safety. In transport they provide energy storage, backup, engine starting and energy recovery. In wind turbines they are important for improving system stability and safety.

Power and energy. Under new power system architectures, grid frequency stability faces greater challenges. On the generation side, supercapacitors smooth the grid connection of wind and solar storage and respond to frequency regulation commands in hybrid storage systems. On the transmission and distribution side they serve substation frequency regulation and distribution terminal backup power, and on the consumption side backup and power supplies. All of these need power type storage devices that deliver short, high power peak pulses, and supercapacitor deployment on the generation, transmission and distribution and consumption sides is already under way.

New energy vehicles. With high power density, high safety, long service life and a wide temperature range, supercapacitors can serve as main power or safety redundant power in 12 V electrical systems, as drive-by-wire power in 48 V systems and as main battery cells in hybrid electric vehicles, improving both performance and safety. As the domestic new energy industry grows, supercapacitors will have even more room to develop.

Transport. Supercapacitors mainly provide energy storage and backup power, engine starting and energy recovery in rail transit, buses, trucks and ships, and can also support specific functions such as generator control gradient and heave compensation on ships and catenary free operation on rail lines. According to Jiushi Bus Group, by the end of 2020 Shanghai routes 930, 17, 18, tunnel line 8 and route 146 had added 89 supercapacitor buses, and together with routes 11 and 26 already in service the city had more than one hundred supercapacitor buses, with six supporting fast charging stations also energised. Future opportunities include golf carts, sightseeing vehicles, airport shuttles and shuttle boats on closed loop routes, a large incremental market. On metro lines, a single line using supercapacitors saves 27,000 kWh per month, about 330,000 kWh per year, with significant economic and environmental benefits.

Wind turbines. Supercapacitors are widely used in wind turbines, and China's wind industry currently demands 500 to 600 million supercapacitors a year. When the grid fails, a supercapacitor can rapidly deliver the large current needed for the turbine to feather its blades safely and shut down, protecting it from damage. Supercapacitors are also widely used to smooth wind farm power output, participate in grid frequency regulation and provide energy recovery and power control. Their high power density, fast response and long life make them vital to wind power systems. A lead acid battery, by comparison, has a short cycle life of 1 to 2 years, typically 300 to 800 cycles, and needs frequent maintenance. A supercapacitor costs three to five times more but is guaranteed free of quality problems for 8 to 10 years, typically achieves more than 500,000 charge and discharge cycles, needs little maintenance and is highly reliable.

Market outlook for supercapacitors

The global supercapacitor market was worth 24.4 billion yuan in 2022 and is expected to reach 71.9 billion yuan by 2029, with Asia Pacific leading at a 39 percent share. The Chinese market reached 3.142 billion yuan in 2022.

Global market. According to QY Research, the global supercapacitor market reached 24.4 billion yuan in 2022 and is expected to reach 71.9 billion yuan by 2029, a compound annual growth rate of 16.5 percent. According to Soochow Securities, Asia Pacific held 39 percent of the market in 2021, ahead of Europe at 36 percent, North America at 20 percent and other regions at 5 percent.

Chinese market. According to Zhiyan Consulting, China's supercapacitor market reached 3.142 billion yuan in 2022, and is expected to expand further as new energy vehicles, smart wearables and similar devices become more widespread.

The global EDLC market was worth 918 million US dollars in 2022, with China at 296 million. In terms of competition, Maxwell of the United States leads with a 32.5 percent share, followed by Elna and Panasonic of Japan.

EDLC market size. According to YH Research, the global EDLC market reached 918 million US dollars in 2022 and is expected to reach 1.392 billion US dollars by 2029, a compound annual growth rate of 6.50 percent. The Chinese market was 296 million US dollars in 2022, about 32.19 percent of the global total, and is expected to reach 466 million US dollars by 2029, when its global share will reach 33.50 percent.

Competitive landscape. The global supercapacitor market is highly concentrated. In 2021 Maxwell of the United States held about 32.5 percent and ranked first, followed by Elna and Panasonic of Japan with 21.3 percent and 16.2 percent. Chinese manufacturers hold a smaller share: Ningbo CRRC and Shanghai Aowei reached 10.2 percent and 8.8 percent respectively in 2021.

In the Chinese supercapacitor market, Maxwell holds the largest share and only Ningbo CRRC can compete with it. The second tier includes domestic manufacturers such as Jianghai, Shanghai Aowei, Kaimei Energy and Fenghua Advanced Technology, while Licong New Energy, Hezhong Huineng and Baina Electric are mainly in the third tier.

Automotive qualification of supercapacitors

AEC-Q certification is the recognised general test standard for automotive-grade components. Supercapacitor manufacturers that want to enter the automotive electronics field and its component supply chain must obtain AEC-Q200 among other certifications.

1. AEC-Q certification is the entry threshold for automotive electronics. AEC stands for Automotive Electronics Council. It was founded in 1994 by Chrysler, Ford and General Motors, and its membership now spans major vehicle makers, automotive electronics companies and semiconductor manufacturers worldwide. Components that comply with AEC specifications can be adopted by all three manufacturers at the same time, which encouraged part makers to exchange product characteristic data, drove standardisation of automotive parts and laid the foundation for the rapid growth of the automotive parts market. AEC-Q is the automotive reliability test standard issued by the AEC and an important passport for part makers entering automotive electronics and tier one supply chains.

2. AEC-Q200 is the entry threshold for automotive-grade passive components. AEC-Q200 is the quality and reliability validation standard issued by the AEC for passive components used in vehicles. It verifies whether passive components can withstand extreme temperature, humidity, vibration and ageing in automotive applications. The standard is intended to prevent performance drift or latent failure in passive components, ensure their quality and reliability, and keep function and performance stable and consistent over continuous use.

3. Products covered by AEC-Q200. Tantalum and niobium capacitors, supercapacitors, ceramic capacitors, aluminium electrolytic capacitors, film capacitors, electromagnetic devices such as inductors and transformers, networks (R-C, C/R), resistors, thermistors, variable capacitors and resistors, varistors, ferrite EMI suppressors and filters, quartz crystals, ceramic resonators and polymeric self-resetting fuses.

4. AEC-Q200 test flow. Revision E defines the test flow explicitly, as shown below.

For lead-free SMD components, special quality requirements apply, and AEC-Q005 defines the reliability issues that arise with lead-free processes, together with the lead-free test requirements. Materials used in lead-free processing include termination plating and board connection solder. These materials usually require higher board connection temperatures to produce acceptable solder joint quality and reliability. The revised AEC-Q200 also states that, to ensure automotive lead-free passive components do not fail after lead-free reflow, certain reliability tests must be completed after reflow before the next step can proceed. Different component sizes also require different numbers of test cycles.

5. NTEK testing capability and AEC-Q200 requirements for supercapacitors. AEC-Q200 qualification for supercapacitors comprises 17 tests. Sample quantities are defined by product size, with the new standard specifying three categories: below 10 cm³, from 10 cm³ to 330 cm³, and above 330 cm³. Larger components require fewer samples. For temperature cycling, for example, a product below 10 cm³ needs 77 samples, one between 10 cm³ and 330 cm³ needs 26, and one above 330 cm³ needs only 10.

About NTEK

NTEK Group was founded in 2009 and is headquartered in Shenzhen. The group provides quality research and technical services covering R&D verification, inspection and testing, failure analysis, simulation and market access for intelligent connected vehicles, electronic communications and new energy.

NTEK has extensive experience in automotive-grade electronic certification and has helped more than 100 companies pass AEC-Q series certification. Driven by the need of vehicle makers to localise automotive-grade components and supported by the domestic semiconductor industry, NTEK provides comprehensive testing and certification services, applying AEC-Q automotive standards to control the safety and quality of automotive components, supporting the growth of domestic automotive-grade components and adding new momentum to the intelligent vehicle safety system.