[Editor's note: In this article we welcome guest blogger Jason Lee, Global Product Manager of Eaton’s Electronic Division.]
Why are so many enamored with supercapacitors?
Chances are you’ve heard mention of supercapacitors if you haven’t yet implemented them in a system design. That’s because when components experience a 30 percent compound annual growth rate, it is usually driven by game-changing advantages.
But what exactly is the potential that supercapacitors promise? As energy storage devices, they offer:
- High power density
- High durability and long life
- 500,000 to 1 million charge/discharge cycles without penalties for deep discharge or high currents
- Up to 20 years' lifetime for backup/UPS applications
- Highly efficient energy transfer, typically greater than 98 percent
- Cost-effective operation in terms of watt-hour cycles or watt-hour years
- Stable performance over a large temperature range
- A green alternative to batteries
Not only are the technical advantages compelling, but evidence suggests that capabilities are evolving rapidly, especially compared to traditional capacitors and batteries. Additionally, costs are coming down, according to market research firm IDTechEx, even as the number of application areas continue to grow.
While battery backup and consumer electronics represent significant share in supercapacitor applications, the large majority of adoptions are for traction motors such as electrically powered rail vehicles, electric locomotives, and trolley buses, as well as vehicles with electric transmission systems such as diesel-electric buses and stop-start cars. Additionally, mobile phones, energy harvesting, renewable energy, and other products of the future will enable this market to grow to more than $11 billion in 10 years, according to IDTechEx.
To be sure, supercapacitors, or ultracapacitors as they are often known and, technically, electrochemical double layer capacitors, are used for energy storage and are not filter components. They are electronic charge accumulators with extreme capacitor-plate-specific area and atomic scale charge separation distance. Unlike batteries, no chemical reactions occur within supercapacitors, and they only store and release energy. Think of them as rechargeable batteries on steroids. While they hold relatively little energy compared to a battery, they can release their energy very quickly. Using another analogy, supercapacitors are like a sprinter with quick bursts who, after short rest, can run again; a battery, on the other hand, is more like a marathon runner.
How do supercapacitors differ from other types of capacitors? Capacitance is measured in surface area over thickness, and supercaps have thickness of greater or less than one nanometer. Supercapacitors have a carbon powder surface area up to 3,000m2 /g. The supercapacitor stores electrons. No reactions take place, so electric charge is available immediately as electrical power. When delivering power, the voltage drops in response to the supercapacitor shedding its storage charge, just like any other capacitor. Due to the very high surface area and molecular scale spacing between capacitor plates, the reaction time is slower than other types of capacitors, but all of the same electrical properties apply.
Supercapacitors have greater power and energy density compared to batteries. It takes 10 hours for a lead-acid battery to deliver a charge produced by a chemical reaction. A supercapacitor could deliver the same charge in as little as 1 second from devices that are much lighter in weight.
Supercapacitors can deliver power at temperatures as low as -40°C as opposed to many batteries, which usually can only operate down to -20°C. They are reliable and predictable in delivering power in conditions up to 85°C whereas batteries are only reliable in conditions up to 60°C.
One of the greatest advantages for supercapacitors is cycle life, because cells can be charged and discharged more than 500,000 times compared to batteries that start to degrade between 300 and 10,000 cycles. Of course, there are several different battery types with varying cycle capabilities. Lead-acid batteries have up to 3,000 cycles; nickel-cadmium has up to 10,000 load cycles; and lithium-ion has up to 10,000 load cycles. Supercapacitors, by comparison, have up to more than 500,000 load cycles.
Supercapacitors can endure from five to 20 years in situations where batteries last from half a year up to only five years.
Additionally, supercapacitors, which are often used in conjunction with batteries, offer various safety advantages, such as the lack of heavy metals used in construction. They meet a variety of environmental and safety standards stipulated by RoHS, SVHC, and UL.
To summarize, the industry’s admiration with supercapacitors is multifaceted. They deliver high power density, high durability and reliability over a greater operating temperature range, and long life in comparison to batteries. Although they are not primary power sources, they offer immense advantages is in terms of safety, cost, weight, and performance for a variety of electronic and electrical systems.