Aug 9, 2009

“Beltway” coating on cathode eases ions’ way into crystalline tunnels

A sample of the MIT battery material that could allow quick charging of portable devices. Credit and Larger Version

April 22, 2009

Lithium iron phosphate (LFP) batteries, first discovered about 10 years ago, already store energy needed to run power tools, medical equipment and plug-in hybrid electric vehicles. LFP batteries are safer, less expensive and more environmentally friendly than most other rechargeable batteries.

But they do have drawbacks, including their slow rate of energy discharge. That means they can’t provide the strong power boost needed for fast acceleration of an electric car, or the quick burst of a metal drill. Now a new technology, developed with support from the National Science Foundation’s (NSF) Division of Materials Research, could speed up the discharge rate of a full LFP battery to only 10 to 20 seconds.

The research took place as part of the Materials Research Science and Engineering Center (MRSEC) at the Massachusetts Institute of Technology (MIT). Gerbrand Ceder, professor of materials science and engineering at MIT, did some calculations and discovered that the cathode material in LFP batteries should be much faster at charging and discharging.

Ceder enlisted MIT graduate student Byoungwoo Kang to help figure out how to “speed up” an LFP battery’s charge and discharge rate.  Their results were reported in a recent issue of the journal Nature.

Why fast discharge?

“When you drive your car at 16 kilometers per hour (10 miles per hour) to go faster, you just push the accelerator,” said Kang. “But if the battery can’t discharge power quickly, there is no acceleration. With this new technology, you can release the power quickly for whatever you need, whether a car or any other application.”

LFP batteries use electrochemical processes to store and release energy. The battery charges up from some energy source, such as an electrical outlet in a garage. Then during discharge, while the battery is in use, the stored energy travels in reverse, providing voltage to run the equipment.

The total amount of energy a battery can hold is called energy density–the higher the density, the more energy it can store.  The power density of a battery is how fast it can supply that energy to the motor or engine that it’s running.

Typically, batteries have a high energy density, but a relatively low power density. This makes them the opposite of supercapacitors, which can store and discharge power quickly, but don’t hold as much as a battery. That’s because supercapacitors can only absorb charge-carrying ions on their surface, while battery materials like LFP can store ions inside their bulk.

“With this experiment, we tried to combine two good things: a strong power density and high energy density,” said Kang. “That means we could use our material as both a battery and a supercapacitor.”

Moving ions

A battery has three parts: a positive cathode, an electrolyte and a negative anode. “Usually the limitations on the battery come from the cathode, and in this experiment we dealt with just that,” Kang said.

While an LFP battery charges, positive lithium ions flow away from the cathode, pass through the electrolyte, and collect on the anode. Then during discharge, the ions reverse direction and flow back to the cathode, where they fit themselves into “tunnels,” or spaces inside the crystal structure.

The energy flowing to the motor from the battery (the electrical discharge rate) is limited by how fast the lithium ions can fit themselves back into the cathode material.

Speeding on the “beltway”

“The LFP usually moves in only one direction, like a one-way highway,” said Kang. “The problem is that the highway is fast, but the tunnel is only wide enough for one ion at a time to get in. So the cars have to wait at the entrance to the highway.”

To speed the ions into the tunnels, the researchers created a special coating on the LFP particles. The coating is a thin, glassy layer–only 5 nanometers thick–on the surface of each particle. This material allows the lithium ions to travel around more easily.

To create the LFP material, the researchers ground up chemicals with a specific ratio of lithium, iron and phosphorus. For this experiment, they changed the ratio of the ions somewhat from the ideal ratio for LFP.

Next, they combined the powders and heated them to 600 degrees Celsius (1,112 Fahrenheit). As the material cooled, a base of stable lithium iron phosphate crystals formed first, followed by the glassy layer coating their surface. The process had the advantage that both the crystal base structure and the surface coating formed in the same step.

According to Kang, the surface layer was like adding a beltway that allowed the ions to travel more quickly inside the cathode material. “With this new, fast lithium conductor, the cars have access from more than one direction into the tunnels,” he said. “One entrance, one highway–a lot of entrances, a lot of highways.”

Bringing it to market

The faster movement of the ions into the crystalline structure is reversible, Kang said, so the new technology works for both fast discharge and fast recharge.

“For the next step, we have to look at how to provide the high power you would need to recharge the battery material this fast,” he said. A standard electrical outlet can’t provide that much energy that quickly, according to Kang, so it would take a network of high-power charging stations, similar to gas stations, to make the new technology practical for plug-in electric vehicles.

Meanwhile, research continues in the lab. “For this experiment, we used a lot of carbon in the cathode, to assure fast charging,” said Kang. “But in a real battery, that is not practical because carbon is bulky and the battery would be too large. We are now trying to reduce the amount of carbon in the electrode to 10 or 15 percent, while keeping the same performance.”

–	Holly Martin, National Science Foundation hmartin@nsf.gov

Investigators
Michael Rubner

Related Institutions/Organizations
Massachusetts Institute of Technology

Locations
Massachusetts

Related Programs
Materials Research Science and Engineering Centers

Related Awards
#0213282 MIT Materials Research Science and Engineering Center
#0819762 MIT Materials Research Science and Engineering Center (MRSEC)

Total Grants
$24,741,002

Related Websites
The Ceder research group: http://ceder.mit.edu/
Nature article: /news/longurl.cfm?id=157
ScienceFriday interview with Gerd Ceder, 3-13-09: http://www.sciencefriday.com/program/archives/200903132
Federal News Radio interview with NSF Program Director for MRSEC, Thomas P. Rieker (3-19-09): http://www.federalnewsradio.com/index.php?nid=14

Aug 9, 2009

Researchers study the feasibility of brains made from carbon nanotubes

Researchers are building mathematical models that accurately reflect neuron connections. Credit and Larger Version

January 27, 2009

Synthetic brains are a long way from reality, but researchers at the University of Southern California, funded by the National Science Foundation, are taking the first steps to build neurons from carbon nanotubes that emulate human brain function.

“At this point we still don’t know if building a synthetic brain is feasible,” said Alice Parker, professor of electrical engineering. “It may take decades to realize anything close to the human brain but emulating pieces of the brain, such as a synthetic vision system or synthetic cochlea that interface successfully with a real brain may be available quite soon, and synthetic parts of the brain’s cortex within decades.”

The challenges to creating a synthetic brain are staggering. Unlike computer software that simulates brain function, a synthetic brain will include hardware that emulates brain cells, their amazingly complex connectivity and a concept Parker calls “plasticity,” which allows the artificial neurons to learn through experience and adapt to changes in their environment the way real neurons do.

There is also the matter of scale. By 2022, with conventional technology, if the team could construct a synthetic brain that emulated real brain function, even crudely, it would take 100 billion artificial neurons and a very a large room to hold them.

“Obviously the technology will have to be downsized to aid a human being or be feasible as a robot brain,” Parker said. Power is another consideration. The power requirements for a synthetic brain are staggering because a human brain never turns off. “In a transistor, things are on or off so it’s a black-or-white situation, but in the brain there are also many shades of gray and power is continuously being consumed,” Parker noted.

But before the researchers can tackle concerns of power and scale, they are building mathematical models that accurately reflect the Byzantine connections of all the neurons and demonstrate how the connections allow neurons to communicate with each other.

Each neuron in the cortex–a part of the brain that contributes significantly to conscious thought and intelligence–is connected to tens of thousands of other neurons. The researchers are also implementing the complex computations carried out by each neuron on all the inputs it receives from other neurons.

“It’s a nonlinear phenomenon and almost impossible to model but that’s what we’re attempting to do,” Parker said.

The researchers have shown that portions of a neuron can be modeled electronically using carbon nanotube circuit models and have performed detailed simulations of the circuit models. A single archetypical neuron, including excitatory and inhibitory synapses, has been modeled electronically and simulated. Parker and her co-researcher, Chongwu Zhou, are in the process of combining these circuit models of neurons to create a functional carbon nanotube circuit model of a small network of neurons. This small network of interconnected neurons will be simulated using the carbon nanotube models. This network demonstrates an interesting neural circuit that detects moving edges in a selected direction.

Parker believes carbon nanotubes are an ideal material to emulate brain function because their 3-D structure allows connectivity in all directions on all planes and because a carbon-based prosthesis is less likely to be rejected by the human body than one made from inorganic materials. But their invasive nature could result in them invading surrounding tissue and prompting lesions and cancers.

“It’s a possibility and something else that needs to be addressed for the technology to be feasible,” Parker said.

As the researchers move ahead with their mathematical modeling and neuron construction, beginning with a single synapse, they ponder “plasticity,” neuroscientists’ term for the brain’s ability to learn and adapt to change. “Our brains can grow new neurons and the synapses between them in an hour–a remarkable biological feature that is difficult to emulate from an engineering perspective,” Parker said.

Emulating such plasticity in a synthetic brain will require a major leap in technology, similar to the leap from cathode ray tubes to transistors. “We don’t know what the new technology will look like yet, but it will be a technology that can self-assemble and reshape itself. As we work in the lab building neurons or constructing mathematical models, we must consider the requirement of plasticity, even if we don’t yet know what it looks like.”

Aside from the daunting technological challenges, a synthetic brain or brain components will also raise ethical and environmental issues. The role of emotions in learning are just beginning to be understood, and it appears they are incredibly important to brain function.

“Based on what I know right now, emotions would have to be included for a synthetic brain to be able to learn,” Parker said. “It’s important to understand their cause and effect.”

–	Diane E. Banegas, (703) 292-8070 dbanegas@nsf.gov

Investigators
Alice Parker
Chongwu Zhou

Related Institutions/Organizations
University of Southern California

Locations
California

Related Awards
#0726815 Biomimetic Cortical Nanocircuits

Total Grants
$359,996

Aug 9, 2009

Nanoparticle test in mice could pave the way for human uses

Bright red-orange photoluminescence observed from porous silicon nanoparticles. Credit and Larger Version

April 30, 2009

The first biodegradable fluorescent nanoparticle to safely image tumors and organs in live mice could be used for cancer detection and treatment in humans.

Chemistry professor Michael Sailor and a team including National Science Foundation- (NSF) supported researchers at the University of California, San Diego (UCSD), report developing the first nanoscale “quantum dot” particle that glows brightly enough to allow physicians to examine internal organs and lasts long enough to release cancer drugs before breaking down into harmless by-products.

The research is another step towards mainstreaming the use of nanotechnology in medicine.  Many researchers say using nanomaterials for medical reasons is the health field’s next major frontier. The payoff, they say, could be lower drug toxicity, lower treatment costs, more efficient drug use and better patient diagnosis.

“There are a lot of nanomaterials that have an ability to do fluorescence imaging,” says Sailor, referring to a useful property that potentially could help doctors further see organs, diagnose patients and perform surgeries. “But they’re generally toxic and not appropriate for putting into people.”

The problem results from toxic organic or inorganic chemicals used to make the materials glow. For example, fluorescent semiconductor nanoparticles known as quantum dots can release potentially harmful heavy metals when they break down. A paramount issue in determining the efficacy of nanomaterials is the body’s ability to harmlessly get rid of residual leftovers after the nanomaterial helps diagnose or treat a disease.

So Sailor’s team designed a new, nontoxic quantum dot nanoparticle made from silicon wafers, the same high-purity wafers that go into the manufacture of computer chips. Researchers took the thin wafers and ran electric current through them drilling billions of pores. They then used ultrasound waves to break the wafer into bits as small as 100 nanometers.

The resulting spongy silicon particles contained nanoscale features capable of displaying quantum confinement effects, or the so-called “quantum dots.” The ones in the UCSD experiment glowed a reddish color when exposed to red, blue or ultraviolet light.

When the nanoparticles were tested in mice, researchers saw tumors glow for several hours, then dim as the particles degraded. The number of nanoparticles dropped noticeably in a week, and they were undetectable after four weeks. They performed a battery of toxicity assays and saw no evidence of toxicity. However, the researchers stopped short of concluding these new nanoparticles were completely harmless.

“Very high doses of any substance can be harmful,” says Sailor. “The important conclusion from this work is that the materials are nontoxic at the concentrations we need to use to see tumors.”

The fact that their quantum dots are made from silicon is key. “A major contributing factor is the fact that these materials degrade into silicic acid, a form of silicon that is commonly present in the human body and that is needed for proper bone and tissue growth,” Sailor says.

Examples where such materials should be useful include the early diagnosis and treatment of cancer. Nanoparticles that glow can reveal tumors too small to detect by other means. During surgery, they can allow the doctor to better find and remove all traces of a cancerous growth. In addition, they can enable targeted delivery of drugs and make it possible to use smaller, safer doses.

Some cancer drugs such as doxorubicin, which is used in chemotherapy, can stick to the pore walls in the new biodegradable nanomaterial and slowly escape as the silicon dissolves. When doxorubicin is delivered to the whole body in doses high enough to be effective, it often has toxic side effects, and its incorporation in the new silicon nanoparticles may provide a more effective, less dangerous way to deliver this important drug.

More needs to be done before this new material can undergo clinical trials in humans. Researchers need to further test its toxicity, how well it delivers drugs to diseased tissues, and how well it can be imaged in clinical settings.

Graduate students Ji-Ho Park and Luo Gu in Sailor’s lab; Sangeeta Bhatia, bioengineering professor at the Massachusetts Institute of Technology and graduate student Geoffrey von Malzahn in Bhatia’s lab; and Erkki Ruoslahti, tumor microenvironment professor at the University of California, Santa Barbara, assisted the research.

Along with NSF, the National Cancer Institute helped fund the research.

–	Bobbie Mixon, National Science Foundation (703) 292-8070 bmixon@nsf.gov
–	David A. Brant, National Science Foundation (703) 292-4941 dbrant@nsf.gov
–	Linda S Sapochak, National Science Foundation (703) 292-4932 lsapocha@nsf.gov

Investigators
Michael Sailor
Sangeeta Bhatia
Erkki Ruoslahti

Related Institutions/Organizations
University of California-San Diego
Massachusetts Institute of Technology
University of California, Santa Barbara

Locations
California
Massachusetts

Related Programs
Biomaterials
Biomedical Engineering
Solid State and Materials Chemistry

Related Awards
#0452579 Chemistry of Nanostructured Porous Si
#9700202 Chemistry of Luminescent Porous Silicon
#9900034 Silicate Phosphors from Sol-Gel Prescursors
#0538512 CAREER: Microscale Structure/Function Studies Towards Development of Engineered Liver Tissue
#0806859 Materials World Network: “New Functionalized Hybrid Systems for Biosensing and drug Delivery”

Years Research Conducted
2008

Total Grants
$1,062,241

Related Agencies
National Cancer Institute

Related Websites
Sailor Research Group: http://sailorgroup.ucsd.edu/
Article in Nature Materials: http://www.nature.com/nmat/journal/v8/n4/full/nmat2398.html

Aug 9, 2009

Segways have had a tough time in big cities, mostly because the city planners can't seem to decide whether they should be ridden on the street or the sidewalk. Here in New York City they remain banned, as their wide stance would be a nightmare on our jammed sidewalks.

The Orbis Urban Mobility Vehicle might be one answer. Looking kind of like a one wheeled Segway, the Orbis' handle can be folded around the wheel, making it somewhat portable. This means that you can hide away your geeky transportation device once you get to work. Unfortunately, you'll still look like a total dork when riding it.