A range of technological advantages makes supercaps or EDLCs (electric double-layer capacitor) an appealing prospect for many applications. These electrostatic capacitors offer superbly low equivalent series resistance values (ESR) and have a stable and effective temperature profile. Their high capacitance and large number of charge cycles allow them to serve as a supplement to batteries (rechargeable or otherwise) and in rare cases to even replace them.
For combining supercaps and Li-ion batteries, Rutronik has specially-patented solutions based on a high-efficiency DC/DC converter topology with ultra-fast switching functions for highly dynamic loads with high peak currents. This involves combining a high-energy store (battery) with a high-performance capacitor (supercap) to essentially emulate a new generation of energy storage facilities while also enjoying the benefits of Li-ion batteries and supercaps. This doubles the life of the battery while offering superb peak currents, and reduces the irreversible losses of Li-ion batteries.
Over the past two decades, suppliers of ultracapacitor cells have invested much in their research & development activities. One of the main goals here has been to gradually increase cell voltage from its original 2.3V. 3V technology is currently at the leading edge. This presents a number of benefits when compared to earlier versions with lower voltages-the higher the voltage, the more energy the cell can hold. Depending on the application, it may even be possible to use fewer capacitors, enabling savings in space, weight and cost. When using the same number of capacitors, the increased service life is a major benefit. It also allows for applications that were previously only feasible with caveats when using supercaps due to the low energy storage, for example when recovering braking energy in vehicles.
The Path to 3V Tech
To achieve a voltage level of 3V, all of the materials must be perfectly adapted to one another. The surface structure of the activated carbon layer and the composition of the electrolyte play an essential role here. To achieve as large a surface as possible, the pore size, pore distribution and pore geometry are improved, as are the chemical surface properties of the carbon material. Adapting the positive and negative carbon layer to the properties of the electrolyte's anions and cations also helps improve voltage potential. This ensures that the proportion of the various charge-bearers to one another is optimized to provide the largest electrical surface available.
This ensures that the cell is also perfectly suitable for the current needs of the industry. In other words, taking into account defined end-of-life criteria, which depending on the supplier may be-as an example-20% capacitance loss and/or an ESR increase of 100%, the 3V cell must offer at least the same service life as a 2.7V cell, which is often 1,500 hours at an ambient temperature of 65°C.
Today, 3V technology is considered "state of the art", and the benefits that it offers allow for greater progress and optimization in projects and the future use of supercaps in various applications.
Offering Longer Service Lives ...
Swapping a 2.7V cell directly for a 3V cell in an existing layout means that you have the same number of components and the same assembly costs, but you also have a significant increase in the life of the supercap. The 0.3V increase in dielectric strength reduces the voltage in relation to the nominal value of the cell, which results in the supercap's life being increased while retaining the same voltage load. For some applications, providing a modicum of extra life may make the difference in allowing these applications to be achieved in the first place. These may be new developments or re-designs that would not have been feasible with previous technical specifications but which can have their service life requirements met with the newer technology. By fitting a 3V cell in an existing, functional layout or design that was previously equipped with 2.7V cells, the application can offer a longer service life than before.
... or Less Space
On the other hand, it's also sometimes worth investigating how many cells are actually needed-especially in circuits where there are many cells connected in series. If the higher voltage makes it possible to reduce the number of components, this provides space advantages that help achieve the miniaturization needed in many applications.
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