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US Navy-led study of ultracapacitors finds Skeleton outperforms Ioxus, Maxwell, JM Energy for transient load applications

Among the new power architectures that hold a great deal of promise are hybrid energy storage modules that integrate energy dense batteries with power dense ultracapacitors (UCs) into a single power supply that augments traditional generation technologies.

Within such an architecture, the UC is the element that may be utilized to sink and source power quickly, at the leading or falling edge of a transient event. UC manufacturers have made considerable advances to increase both the power and energy density of UCs. Significant reduction of the internal impedance has resulted in an increased power capability that makes UCs well suited for use in these applications.

A study led by John Heinzel from the US Naval Surface Warfare Center in Philadelphia, along with researchers at the University of Texas at Arlington, has compared the performance of UCs from four different manufacturers: Maxwell, Ioxus, JM Energy, and Skeleton.

The team studied cells from the four different manufacturers under high pulsed load conditions to measure their power density into low-impedance loads.

The researchers found that the Skeleton cell far outperformed the other cells tested. Their paper is published in the IEEE Transactions on Plasma Science.

Its [the Skeleton cell] ESR was less than half of any of the other cells tested, and its power density is more than 10-kW/kg higher than the others. As for the JM Energy cell, it was the least power dense and had the highest ESR of the four cells tested. This was as expected due to its properties as an LIC, though it is more energy dense than the other three cells as well.

Skeleton’s superior results are likely due to their use of curved graphene instead of the activated carbon that the other manufacturers use. This advancement in the energy storage technology will allow for the construction of energy systems that can supply more power to transient loads and allow for the reduction in the size of existing systems. It also allows for more efficient energy storage systems due to the cell’s low ESR. Future testing will include repetitive pulsing that will be used to compare the amount of energy lost as heat for each cell due to their ESR.

—Nybeck et al.


  • Charles N. Nybeck, David A. Dodson, David A. Wetz, John M. Heinzel (2019) “Characterization of Ultracapacitors for Transient Load Applications” IEEE Transactions on Plasma Science doi: 10.1109/TPS.2019.2904562



Good news for high power graphene super caps. Combined with recent high energy batteries, it could recuperate more deceleration/braking energy to extend max range.? Also ideal for grid leveling and fixed storage units.


Low resistance so low losses operating in much shorter time and accompanied by high number of cycles are the prize.
More recently with the increased interest in energy saving and timing we see many new applications proven. Increasing use in everyday commercial applications can't be far away.


The Navy find them best for their needs, but could be they have a low cycle life, or too high a cost factor or some other reason not to work for some other applications like in EVs. Temperature range? Expansion under load?


It states half the resistance (esr) and higher energy density by 10 kW (sec?) than traditional activated carbon designs.
Military specs are usually seen as most demanding.
'Curved graphene' as referred to is but one of many structured carbon materials that are under examination for improved capacitor performance in electrical and electronic applications.
The ability to build such and many other scaffold structures utilising a variety of imaginative ' nano technology' techniques has promise to creating materials with properties we /they (engineers chemists and physicists) could previously only dream of.


LIC = Lithium Ion Capacitor


These results are unsurprising.  The UC market has niches for different purposes; fast-acting energy stores for e.g. servomotor controllers require maximum specific power, while soaking up the regenerated braking energy of a hybrid bus takes place over several seconds and makes more demands on energy density.

Horses for courses.

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