Review: The development of supercap technology
Supercap technology, also known as Electric Double Layer Capacitors (EDLC), has made remarkable progress in recent years. Supercaps are also known as EDLCs, ULTRACAPs, supercapacitors, doublelayercondensers or "supercap" for short. These are condensers with an electrolyte and carbon electrodes as the electroconductive layer. Compared to conventional condensers, they have a significantly larger surface area, which leads to a higher capacity. The technical and physical principles are very well described in the literature (see Wikipedia). The variety of terms for this type of capacitor is further extended by manufacturers' own terms:
- Goldcap™ [Panasonic]
- Boostcap™ [Maxwell]
- Greencap™ [Samwha]
- PURIXEL™ [Pureechem] for supercap cells
- PURETRON™ [Pureechem] for supercap modules
It all started in Germany with NESSCAP
For CAPCOMP, the story in Germany started in 2005 when we signed a contract with the South Korean company NESSCAP, which emerged from the DAEWOO Group. At that time, the idea was still to use EDLCs as the primary energy storage device in cars. It was hoped that the development of the technology would progress in a similar way as semi-conductor technology had done for years. Unfortunately, this remained a dream.
Electro chemistry and the associated physical principles quickly revealed limits. At the beginning of the 2000s, there were various prototype developments in the USA for use in electrically operated vehicles. Tests at the University of Vermont showed that battery-powered vehicles supported by ULTRACAPs achieved about 35% - 40% more range, depending on the driving cycle.
No less interesting were the results confirming an increase in battery life where power peaks were absorbed by ultracapacitors.
In addition to high expectations on the part of the automotive industry, there was also scepticism, as the AECQ200 test results did not yet provide enough data from which binding technical specifications could be derived. As distributors from the beginning, we and our competitors had no choice but to define criteria based on those of electrolyte capacitors and to test according to them.
Times of complex tests under extreme conditions
Dozens of test series were set up for the most diverse applications. Even the behaviour of the ultracaps in a vacuum and at extreme minus temperatures was examined. The cells were frozen to -60°C, thawed, tested - and passed! No negative change in the technical properties. Just like practical tests in vehicles tested at 3500 m above sea level at -25°, like the application in a car after it had been standing at the airport in the sun in Jeddah, Saudi Arabia, for 5 days. In addition, acceleration tests, vibration tests, fire load and emission tests, as well as durability tests under a wide range of conditions provided valuable insights. For example, single-cycle tests to assess the cells under a specific load behaviour took half a year to produce initial results. These tests were then continued for another 6 months to obtain a reliable database.
MAXWELL, NESSCAP and PANASONIC made the start
It was the companies MAXWELL, NESSCAP and PANASONIC, as the main players in ultracap development, who were instrumental in driving the acceptance of this new technology. Other manufacturers followed and built on this experience. In principle, the requirements of the market have not changed since the first hour.
From the prismatic cell to the high-voltage ultracap module
At the beginning (Vermont tests), prismatic cells with up to 5000F and 2.7 volts were still used. In the early phase, this technology was considered a promising solution, but then quickly showed physical weaknesses, especially in heat distribution. In manufacturing technology, it turned out to be too complex and costly for large-scale production.
Great progress in module development
With the development of the 60mm cylindrical, axial 3000F/2.7V cell, it became possible to develop high-voltage cells and high-energy modules. These cells could store and return large amounts of power quickly, with high reliability and cycle stability of over one million cycles. The horizontal heat distribution and much better thermal resistance than previous models allowed for more efficient thermal management. Different models of modules were created for a wide range of applications.
Recuperation solution for trucks
After some time, the 125V/62F module became an industry standard in buses and trains in several variants. For recuperation, i.e. energy recovery from braking energy, the modules proved to be the ideal solution; even better than for passenger cars. Not only because of the more relaxed situation with regard to installation space, but above all because of the better cost/benefit ratio.
Shorter payback times for recuperation technology in trucks
Commercial vehicles are usually operated much more intensively than passenger cars. The investment in an ULTRACAP recuperation system could therefore pay for itself much more quickly. In city buses and trams, the modules were already widely used about 15 years ago and are only now reaching their service life limit. Several 125V/62F modules were connected in series/parallel. They were usually mounted on the roof or in the underbody of the vehicle. The balancing of the modules within themselves and among each other was done via "Smart Balancing". Data was sent via CAN-BUS interfaces to central ECUs for further evaluation and control. The smaller 48V/165F modules, also based on the 3000F/2.7 volt cells, are still an industry standard today.
48V/165F ultracap modules in driverless transport systems
They are used extensively in Automated Guided Vehicles (AGVs), but are suitable for all universal energy storage systems. They are easy to configure in series-parallel circuits and also easy to handle due to their relatively low weight of approx. 15kg. In addition, there are now a large number of variants in a wide range of voltages and capacities, which are used depending on the application.
The next step in development: 3 volt cells
In the meantime, 3V cells in the identical form factor as the cells of the 2.7V technology are increasingly gaining acceptance. These are still a little more expensive than the older types, but it is a matter of time before only 3V technology dominates. Today, almost 20 years after the early walking attempts with electrically assisted drive systems based on ultracap, we are entering a new phase. Fully electric vehicles with lithium-ion batteries have already been the new standard for passenger cars for several years.
Fuel cell & ultracap: dream combination of tomorrow?
In commercial vehicles, there are already the first vehicles with this combination. But here, too, the discussion about whether hydrogen technology in combination with fuel cells and ULTRACAPs will be used on a large scale as a fast high-performance energy storage system is not over. The first commercial vehicles are already being tested. There are now new hybrid technologies that allow capacities of up to 100.000 farads. It remains exciting!
The most important technical development steps of ultracaps
- Electrode material : Instead of activated carbon, matierials such as carbon nanotubes and graphene are now used. These materials offer a larger surface area and enable a more efficient charge and discharge rate.
- Electrolytes with higher conductivity and greater dielectric strength : New materials such as ionic liquids and conductive polymers have significantly improved the performance of supercaps. This led to increased energy density and enabled their use in more demanding applications.
- Miniaturisation of supercaps : An important step towards economic significance. Advances in manufacturing technology have enabled smaller and more compact supercaps to be produced for use in electronic devices such as mobile phones, laptops and cameras. This development has led to increasing demand and increased market penetration of the technology.
- Improving the lifetime of supercapacitors : By optimising cycle stability and reducing capacity loss, reliability and lifetime increased. This made them more attractive for applications such as energy storage in renewable energy systems and electric vehicles.
- Economies of scale and improved production efficiency : The reduction of manufacturing costs had a major impact on the worldwide diffusion of supercaps. Increasing production volumes and the increased use of supercaps in various industries have led to a competitive market and improved availability.