“Back to the Future” ~ Nanotechnology offers new approach to increasing storage ability of Capacitors: Applications for Portable Electronics & EV’s

back-to-the-future-bttf2For Back to the Future fans, this week marked a milestone that took three decades to reach.

Oct. 21, 2015, was the day that Doc Brown and Marty McFly landed in the future in their DeLorean, with time travel made possible by a “flux capacitor.”

While the flux capacitor still conjures sci-fi images, capacitors are now key components of portable electronics, computing systems, and electric vehicles.

In contrast to batteries, which offer high storage capacity but slow delivery of energy, capacitors provide fast delivery but poor storage capacity.

A great deal of effort has been devoted to improving this feature — known as energy density — of dielectric capacitors, which comprise an insulating material sandwiched between two conducting metal plates.

Now, a group of researchers at the University of Delaware and the Chinese Academy of Sciences has successfully used nanotechnology to achieve this goal.

dialectric Capacitor id41672.jpgDielectric Capacitor: A diagram of the dielectric capacitor research developed by a University of Delaware-led research team.

The work is reported in a paper, “Dielectric Capacitors with Three-Dimensional Nanoscale Interdigital Electrodes for Energy Storage”, published in Science Advances, the first open-access, online-only journal of AAAS.

“With our approach, we achieved an energy density of about two watts per kilogram, which is significantly higher than that of other dielectric capacitor structures reported in the literature,” says Bingqing Wei, professor of mechanical engineering at UD. (Article continues below)

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(Article Continued from above)

“To our knowledge, this is the first time that 3D nanoscale interdigital electrodes have been realized in practice,” he adds. “With their high surface area relative to their size, carbon nanotubes embedded in uniquely designed and structured 3D architectures have enabled us to address the low ability of dielectric capacitors to store energy.”

One of the keys to the success of the new capacitor is an interdigitated design — similar to interwoven fingers between two hands with “gloves” — that dramatically decreases the distance between opposing electrodes and therefore increases the ability of the capacitor to store an electrical charge.

Another significant feature of the capacitors is that the unique new three-dimensional nanoscale electrode also offers high voltage breakdown, which means that the integrated dielectric material (alumina, Al2O3) does not easily fail in its intended function as an insulator.

“In contrast to previous versions, we expect our newly structured dielectric capacitors to be more suitable for field applications that require high energy density storage, such as accessory power supply and hybrid power systems,” Wei says.

Source: By Diane Kukich, University of Delaware

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UC San Diego: Increasing Energy Storage Capacity: Charged “Holes” in Graphene: Applications: Cars, Wind Turbines, Solar Power

UC San Diego 0422 chargedholesEngineers at the University of California, San Diego have discovered a method to increase the amount of electric charge that can be stored in graphene, a two-dimensional form of carbon. The research, published recently online in the journal Nano Letters, may provide a better understanding of how to improve the energy storage ability of capacitors for potential applications in cars, wind turbines, and solar power.

Capacitors charge and discharge very fast, and are more useful for quick large bursts of energy, such as in camera flashes and power plants. Their ability to rapidly charge and discharge is an advantage over the long charge time of batteries. However, the problem with capacitors is that they store less energy than batteries.

How can the of a capacitor be improved? One approach by researchers in the lab of mechanical engineering professor Prabhakar Bandaru at the Jacobs School of Engineering at UC San Diego was to introduce more charge into a capacitor electrode using graphene as a model material for their tests. The principle is that increased charge leads to increased capacitance, which translates to increased energy storage.

How it’s made

Making a perfect carbon nanotube structure ― one without , which are holes corresponding to missing ― is next to impossible. Rather than avoiding defects, the researchers in Bandaru’s lab figured out a practical way to use them instead.

“I was motivated from the point of view that charged defects may be useful for energy storage,” said Bandaru.

The team used a method called argon-ion based plasma processing, in which graphene samples are bombarded with positively-charged argon ions. During this process, carbon atoms are knocked out of the graphene layers and leave behind holes containing positive charges ― these are the charged defects. Exposing the graphene samples to argon plasma increased the capacitance of the materials three-fold.

Charged holes in graphene increase energy storage capacity
Zigzag and armchair defects in grahene

“It was exciting to show that we can introduce extra capacitance by introducing charged defects, and that we could control what kind of charged defect we could introduce into a material,” said Rajaram Narayanan, a graduate student in professor Bandaru’s research group and first author of the study.

Using Raman spectroscopy and electrochemical measurements, the team was able to characterize the types of defects that argon plasma processing introduced into the lattices. The results revealed the formation of extended defects known as “armchair” and “zigzag” defects, which are named based on the configurations of the missing carbon atoms.

Additionally, electrochemical studies helped the team discover a new length scale that measures the distance between charges. “This new length scale will be important for electrical applications, since it can provide a basis for how small we can make electrical devices,” said Bandaru.

Explore further: The chemical battle inside instantaneous energy storage devices

More information: “Modulation of the Electrostatic and Quantum Capacitances of Few Layered Graphenes through Plasma Processing.” Nano Letters 2015. DOI: 10.1021/acs.nanolett.5b00055

Can capacitors in electrical circuits provide large-scale energy storage?

Capacitors electricalciCapacitors are widely used in electrical circuits to store small amounts of energy, but have never been used for large-scale energy storage. Now researchers from Japan have shown that the right combination of resistors and capacitors can allow electrical circuits to meet two key requirements of an energy storage device: quick charging and long-term discharging. Using capacitors as energy storage devices in circuits has potential applications for hybrid electric vehicles, backup power supplies, and alternative energy storage.

The researchers, Prof. Mikio Fukuhara, Tomoyuki Kuroda, and Prof. Fumihiko Hasegawa, at Tohoku University in Sendai, Japan, have published their paper in a recent issue of Applied Physics Letters.

Developing efficient methods of is a major topic of research, with a strong focus on batteries, fuel cells, and electric double-layer capacitors (EDLCs) when not incorporated in circuits. So far, no research has been performed on the use of capacitors or supercapacitors as energy storage devices in circuits.

To explore the possibility of using capacitors to store energy in circuits, the researchers investigated the charging/discharging behavior of 126 resistor-capacitor (RC) combinations of 18 resistors, three ceramic capacitors, and four aluminum capacitors. They found that the RC combinations that are the best in terms of quick charging and long-term discharging consist of circuits with a small resistor, a large resistor, and a large capacitor. Some of these circuits could be charged in less than 20 seconds and hold the charge for up to 40 minutes, while having relatively large capacitances of up to 100 milliFarads (mF).

How to quickly store a large amount of electricity and control long-term discharging in an electrical circuit: (a) The capacitor (C) is quickly charged by closing switches S1, S2, S3, and S4. (b) To store the electricity in the capacitor, …more

“The greatest significance of this work is the discovery of an RC region that offers quick charging and long-term discharging in an electrical circuit,” Fukuhara told Phys.org. “We think that this system will become an important method for storing much energy or only small amounts of energy in the near future. For this purpose, the storage must change from an electrochemical to a physical device.”

The researchers attribute the quick charging and long-term discharging to the damming effect of the large resistor in the circuit. They explain that the relationship between the resistance and the capacitance of a supercapacitor is similar to that between the plug size and the amount of water in a water tank. The larger the plug (resistor), the more water (capacitance) the tank can hold. Until now, the damming effect of this RC combination on storage in such circuits has been overlooked.

Capacitors electricalci

The results also showed that a “dry” or “solid” supercapacitor made of an amorphous TiO2 surface with nanometer-sized cavities provides better performance than typical supercapacitors that use liquid solvents. The researchers’ earlier work on these dry TiO2 capacitors showed that they have several advantages for energy storage, such as a large capacitance of 4.8 F, wide operating temperature range from 193 to 453 K, and large voltage variation from 10 to 150 V. In contrast, traditional EDLCs suffer limitations in all of these areas.

“Besides the early original researchers of electric circuits, people have believed that circuits are used only for quick charging and prompt discharging,” Fukuhara said. “Consequently, the damming effect of this RC combination on electrical energy storage in such has been overlooked. When we began researching the dry physical capacitance using solid materials only, we began questioning the usual usage of capacitors based on the conventional concept.”

In the future, the researchers plan to work on further improving the performance of these dry supercapacitors in order to make improvements to the system overall.

“Our plans are to develop dry, physical electric for use by electric vehicles, AC transmission lines, and charging of large amounts of lightning or large amounts of currents stored in air,” Fukuhara said. “However, it will take a long time.”

Explore further: Energy storage in miniaturized capacitors may boost green energy technology