Is speed more important than storage with Ultracapacitors?




Ultracapacitors powering next-generation electronic devices

Ultracapacitors. Chemical batteries drive a plethora of mobile electronic devices, but frequent repeated cycles of charging and discharging degrade the battery over the life of the device. An alternative energy storage device known as an ultracapacitor can be recharged hundreds of thousands of times without degrading. A research group from the University of West Florida (UWF) published a paper this week in the American Institute of Physics’ Journal of Renewable and Sustainable Energy describing an ultracapacitor that was fabricated and tested which maintains a near constant voltage. This highly innovative constant-voltage design has the potential to enable the application of ultracapacitors in low-voltage electric vehicle circuits and mobile electronic devices.

Standard capacitors store energy in an electric field created when opposite electrical charges congregate on two plates separated by a thin insulator material. In contrast, for ultracapacitors, the surface area of the plates is increased with a coating of porous carbon, which is filled with tiny holes and cracks that can capture charged particles. The space between the plates is filled with an electrolyte solution containing positive and negative ions. As charge accumulates on the plates, they attract ions, creating an additional layer of stored energy. In both standard capacitors and ultracapacitors, the voltage drops as the stored charge is released, but the majority of electronic devices require constant voltage to function properly. An electronic circuit called a DC-DC converter can alter the falling voltage of the capacitor into a constant voltage output, but the converters on the market are typically unstable below one volt.

Therefore, the UWF team designed an ultracapacitor that maintains a near-constant voltage without a DC-DC converter. This device is connected to an electromechanical system that can slowly lift the core of the device out of the electrolyte solution as the stored charged is released. As the electrolyte drains away, the device holds less charge; thus, lowers its capacitance. Since the voltage of the capacitor is related to the ratio of the stored charge to the capacitance, the system maintains a steady voltage as charge leaks away. Testing by the UWF group showed that the constant-voltage mechanism operates with a 99 percent efficiency or higher. The lifetime of the electromechanical motor is expected to be about the same as the lifetime of the ultracapacitor’s core, which would dramatically improve the robustness and performance of next-generation power storage devices.

The ultracapacitor has many advantages over current advanced battery technology and has the potential to revolutionize electronic devices and car batteries. In addition to their near limitless ability to be recharged, ultracapacitors can release energy much faster than common batteries.

There are many other interesting commercial applications for ultracapacitors. For example, they can aid in significantly reducing battery recharge times. Fully recharging the battery in a household power tool such as a drill or saw can take several hours, even if the tool is only used on a project for a few minutes. However, when an ultracapacitor is combined with a lithium-ion battery, power tools could be recharged in about one minute and have a lifetime of more than 20,000 charges. One current disadvantage of commercially available ultracapacitors is that they store only a fraction of the energy per unit mass that batteries store. As a result, it would only allow a power tool to run for only about 10 percent as long as it would on a normal battery, but research at institutions such as Arizona State University in Tempe, Arizona are focused on overcoming this limitation.


Is speed more important than storage with Ultracapacitors?


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