You are browsing the archives of 2011 November.

Electrochemical capacitors—also called supercapacitors or ultracapacitors—have received a lot of attention in the past decade or so for energy storage because of their ability to deliver large amounts of energy quickly. Batteries, on the other hand, store large amounts of energy, but delivery it slowly.

In a short paper in Science, researchers Gogotsi and Simon, note that some recent papers report energy densities for ECs that are near or even better than the energy densities of batteries. In their paper, they warn that it is important to be careful about comparing metrics. It matters, they say, because “even when some metrics seem to support these claims, actual device performance may be rather mediocre.”

Energy storage devices can be compared using Ragone plots, which map power density (the rate of charge/discharge) against energy density (the storage capacity). The densities are usually presented as weight-based quantities, which Gogotsi and Simon observe may not be accurate for assembled devices “because the weight of the other device components also needs to be taken into account.” Those other components are the same as the components that comprise a Li-ion battery-current collectors, electrolyte, separator, binder, connectors, packaging and carbon-based electrodes.

The carbon electrodes contribute about 30 percent of the total mass of a commercial EC, which means “the energy density of 20Wh/kg of carbon will translate to about 5 Wh/kg of packaged cell.” However, carbon electrodes that are thinner or lighter will reduce energy density even more. For example, an electrode made of the same carbon material as a commercial electrode, but 10 times thinner or lighter, reduces energy density by about one-third, so the 5Wh/kg is reduced to 1.5 Wh/kg.

Gogotsi and Simon make the case that comparing energy and power densities on a volumetric basis would eliminate uncertainty and confusion about performance metrics for ECs. Nanomaterials have a very low packing density, leaving a lot of empty space which the electrolyte can flood, thus increasing the weight of the device without contributing any capacitance. Also, they note that the smaller the device, the less meaningful weight-based metrics are, simply for lack of mass. For example, a carbon nanotube coating electrode contributes negligible weight to the device.

“These systems may show a very high gravimetric power density and discharge rates, but those characteristics will not scale up linearly with the thickness of the electrode, i.e., the devices cannot be scaled up to power an electric car,” they say in the paper.

The authors also caution against relying too heavily on Ragone plots because they convey no information about other important device performance metrics such as cycle lifetime, energy efficiency, in-service temperature range, cost, etc.

The authors conclude with a call to action to the electrochemical energy storage device research community to present energy and power density data in a consistent manner. And, they recommend setting up national and international testing facilities for benchmarking electrodes and EES devices similar to those that exist for evaluating photovoltaics.

“Clear rules for reporting the performance of new materials for EES devices would help scientists who are not experts in the field, as well as engineers, investors, and the general public, who rely on the data published by the scientists, to assess competing claims,” they conclude in the paper.

The paper is “True Performance Metrics in Electrochemical Energy Storage,” Y. Gogotsi and P. Simon, Science, 18 Nov. 2011 (doi: 10.1126/science.1213003)

Share

Steve Bossart of DOE’s NETL describes the characteristic features and advantages of a smart grid infrastructure in this interview. Click on the image to link to the video. Credit: DOE NETL.

So much materials science research and news revolves around energy and its generation, storage and efficient use. It’s easy to overlook materials issues relating to the delivery of electricity, especially the “smart grid.”

Steve Bossart of DOE’s NETL will be giving an invited talk on materials for the smart grid at the Materials Challenges in Alternative and Renewable Energy meeting Feb. 26-March 1, 2012 in Clearwater, Fla.

Based on the abstract of his talk, materials research for the smart grid falls into two categories: Using electricity better and managing electricity delivery better. The latter include devices like solid-state circuit breakers, relays and switches, solid-state transformers, current limiters, static VAR compensators, high-voltage direct converters and AC/DC inverters.

Bossart explains the smart grid in a 2009 interview with Joe Culver, which is posted on the NETL website. The video is a little long, almost 18 minutes, but Bossart provides a clear description of what a smart grid is, how a smart grid improves on the current power delivery system, the business case for smart grid power delivery and more. His descriptions of an intricate infrastructure system are well organized and easy to follow.

He begins by defining a smart grid, “We tend to think of the smart grid in terms of its functionality instead of a specific group of technologies. A specific group of technologies limits you in terms of what you can do with a smart grid.” He goes on to describe seven functionalities of a smart grid. A smart grid, he says,

1. Enables consumer participation in the grid,
2. Accommodates all kinds of storage and generation options in a plug-and-play mode,
3. Enables new products, services and markets,
4. Provides power economy needs of a digital society,
5. Optimizes assets already on the grid system and operates them more efficiently,
6. Anticipates and responds to disturbances,
7. Has operation resiliency to attack and natural disasters.

Bossart develops each of these points (and others in the video) with enough detail to educate the viewer without wandering too far into technical specifics.

The MCARE meeting is organized into 11 symposia, including one on the electric grid. Organizers are putting the program together now, and it should be available by Dec. 14, 2011. The other symposia are Batteries and Energy Storage, Biomass, Geothermal, Hydrogen, Hydropower, Materials Availability for Alternative Energy, Nanocomposites and Nanomaterials for Energy, Nuclear, Solar Power and Wind.

Abstracts for the six plenary talks are available on the website, as is the list of invited speakers for the symposia.

Here is the full abstract of Bossart’s invited talk:

TITLE: Materials Research for Smart Grid Applications

ABSTRACT: Our nation is transitioning to a Smart Grid, which can sense and more optimally control the transmission, distribution, and delivery of electric power. The control of the electric power system is becoming more challenging with the addition of distributed renewable power sources, energy storage systems, electric vehicle charging, building and home energy management systems, smart appliances and devices capable of demand response, and other technologies. These assets coupled with a smarter grid can provide many benefits including reducing peak demand and electricity consumption; better efficiency and reliability in distribution network, remote meter reading, improved outage management, automated feeder reconfiguration, improved maintenance by monitoring equipment health, and providing ancillary services to enhance grid stability and reliability. Materials research can enhance many applications made possible by smart grid. Materials research can result in reduced cost, increases in operating voltage and current, faster switching and sensing speed, better thermal management, greater efficiency, better protection, and longer life for many devices including solid-state circuit breakers, relays and switches, solid-state transformers, current limiters, static VAR compensators, high-voltage direct converters, and AC/DC inverters.

Share

Check ‘em out:

Ultralight metallic microlattices

A team of researchers from UC Irvine, HRL Laboratories and the California Institute of Technology have developed the world’s lightest material—with a density of 0.9 mg/cc—about 100 times lighter than Styrofoam. Their findings appear in the Nov. 18 issue of Science. The new material redefines the limits of lightweight materials because of its unique “micro-lattice” cellular architecture. The researchers were able to make a material that consists of 99.99 percent air by designing the 0.01 percent solid at the nanometer, micron and millimeter scales. The material’s architecture allows unprecedented mechanical behavior for a metal, including complete recovery from compression exceeding 50 percent strain and extraordinarily high energy absorption.

Researchers find way to create cheap thermoelectric materials

A team led by Dr Ole Martin Løvvik of Oslo University’s Centre for Materials Science and Nanotechnology in Norway has been studying the thermoelectric effect at the nanoscale for several years. The key to the problem is that a good thermoelectric material ought to have high thermal resistance but low electrical resistance. Therefore, perhaps counter-intuitively, it is important to prevent heat dissipation through the material. The fabrication method involves cooling down blocks of semiconducing materials to -196°C with liquid nitrogen to make them more brittle and less sticky, then grinding them down into nanoscale particles using a ‘mill’. These particles are then essentially compressed back together in a controlled fashion, leaving the essential nanoscale barriers.

Cheers and applause as £4 million neutron instrument is lowered into place

Engineers and scientists at the UK Science and Technology Facilities Council’s ISIS neutron source faced nervous moments on Friday (11 November 2011) when a new £4 million instrument that took five years to design and build, was lifted and lowered into its fixed position by a 30 tonne crane. Polaris, a ‘super microscope’ is one of the most advanced neutron instruments in the world. It will measure objects on the nanometre scale, a million times smaller than a speck of dust. The giant camera will make images of the atomic structure of materials and will be able to watch chemical reactions in real time. Measuring the positions of atoms in a material allows you to understand completely why a material behaves the way it does.

Architecture and ceramics: A material for all the ages

Architecture and Ceramics: A Material For All The Ages is currently running through Dec. 17, 2011 in the HGA Gallery, Rapson Hall of the Goldstein Museum of Design (University of Minnesota). Architecture and ceramics are fundamental cultural forms. The kinship between architecture and ceramics draws upon the physical materials they use and the formal and conceptual problems they address. Ultimately, however, what binds them together is their shared connection with human use, and human life-and art. This exhibition uses photographs to illuminate the rich and complex relationship between architecture and ceramics from the ancient world to the present.

Engineers test wireless LED contact lens on a living eye

Engineers from the US and Finland have tested a wireless contact lens featuring a working LED light on a living eye for the first time. Although the proof-of-concept device only contained a single pixel, it could pave the way for lenses that display emails and text messages directly to the wearer’s eyes or provide real-time health monitoring information such as glucose levels. The lens—developed by researchers at the University of Washington and Aalto University—consists of an antenna that receives power in the form of radio waves, an integrated circuit to store the energy and a transparent sapphire chip containing a single blue LED.

Share

This video shows the 3D printing process used to fabricate ceramic espresso coffee cups designed by Bernat Cuní. Credit: Shapeways; YouTube.

Additive manufacturing and rapid prototyping technologies are gaining ground as advanced manufacturing methods. Just last week we reported on solid freeform fabrication of one-piece fused silica molds for investment casting.

Artistic minds have also discovered the versatility of additive manufacturing.

Gizmag reports on a project by Spanish designer Bernat Cuní to create 30 unique espresso coffee cups in 30 days using 3D ceramic printing. On his website, Cuní describes himself as “Currently engaged in experimenting [with] the fields of generative design, creative code and rapid manufacturing. I’m particularly interested in the future of design and the popularization of the design process and tools.”

In the story, Cuni says he began the project as a proof-of-concept, using additive manufacturing “in order to achieve something unthinkable some time ago: Create a product from the idea to the consumer in less than 24 hours.” The story describes the project.

Construction of each cup takes about four hours and begins with the deposition of an organic binder on a bed of ceramic powder. Once that layer is completed, more ceramic powder is distributed on top, then more binder and so on until the model is complete. The entire matrix is then heated in an oven, which solidifies the binder-laden powder. The unbound ceramic material is then cleaned away from the solidified cup and it’s prepared for the next several steps in the process.

At this point, the cup is solid but delicate, and so must be fired in a kiln at high temperature to permanently lock in the structure. The piece emerges with a rough surface, which is pre-glazed with a water-based spray, then re-fired in the kiln at a lower temperature. This smooths the surface a bit and paves the way for the final glaze coat, which is sprayed on, as well. After the final firing, the cup takes on that familiar shiny, durable surface we’ve come to expect from traditional ceramics.

The full collection can be viewed at Cuní’s website, where he has posted a gallery showing each day’s cup, beginning with Day 00, the Basic cup. The designs are funky and fun, and their titles are just as delightful. Check out, for example, the Klein Bottle cup, the Helveticup or the Octo cup.

If you need to have one, visit the website of Shapeways, a partner with Cuní. Shapeways is a start-up company that specializes in customized 3D printing. According to their website, “we’re bringing personalized production to everyone.”

The cups are small (about 1.5 inch diameter), food-safe, heat-resistant, recyclable and glazed, but not cheap. Prices range from $36 to $81. .

Share