 |
|
Self-Assembling Batteries Link Yet-Ming Chiang, a professor of materials science at MIT, and his colleagues selected electrode and electrolyte materials that, when combined, organize themselves into the structure of a working battery. The researchers had been looking for ways to exploit short-range forces between micro- and nanoscale particles. After measuring such forces between materials using ultraprecise atomic-force microscope probes, they were able to select materials with just the right combination of attractive and repulsive forces. As a result, similar materials clustered together to form opposite electrodes, while a gap necessary for the battery to function was maintained between the electrodes. The work is the cover story in the current issue of Advanced Functional Materials. Self-assembly is attractive because it could potentially reduce manufacturing costs and allow molecular-level control of the structure of the batteries, leading to materials and devices not easy to make using conventional manufacturing methods. Self-assembly has already been used to create a number of materials and a handful of simple devices, including half a battery. (See "Powerful Batteries That Assemble Themselves.") "Ultimately, the goal is just to chuck a bunch of stuff into a bucket and have it self-assemble into a battery," says Jeff Dahn, professor of chemistry and physics at Dalhousie University, in Canada. Chiang's work creating a prototype self-assembling battery is "really nice science," Dahn says. "Just the fact that you can do it is pretty cool." The researchers faced a number of challenges in designing the self-assembling batteries. They are limited to materials with the electrochemical properties necessary for battery electrodes. And within each electrode, the particles need to pack together tightly, which can be accomplished if they are attracted to each other. The particles must also be attracted to materials that conduct electrons to and from the electrodes. Most important, the battery's two electrodes need to be kept separate--a challenge because they are oppositely charged and therefore tend to attract each other. By relying on their new understanding of short-range forces, Chiang and his colleagues were able to select two electrode materials that, at very short distances on the order of a couple dozen nanometers, had surface repulsive forces greater than their attractive forces. As a result, there is always a space left between the electrodes. The researchers used lithium cobalt oxide and microbeads of graphite for the electrodes--materials commonly used in lithium-ion batteries--pairing them with a carefully selected liquid electrolyte. The electrolyte serves as an insulator, allowing ions to shuttle between the electrodes but forcing electrons to move through an external circuit, where they can be used to power a device. In the researchers' prototype battery, the graphite microbeads pack together to form one electrode and connect to a platinum current collector, all the while staying clear of the lithium cobalt oxide that forms the other electrode. The researchers tested the battery and showed that it could be both discharged and recharged multiple times. The extent to which such batteries will find commercial applications is unclear. Dahn points out that in manufacturing today's batteries, the electrode materials are compressed under enormous pressures to ensure as great as possible energy storage. Such forces could not be applied to a self-assembled battery, so Dahn says it will be "very tough" to compete with conventional batteries in terms of energy capacity and maybe even in terms of cost. Dahn also notes that challenges still remain before such batteries can be commercialized. For example, it is still necessary to find a way to package the self-assembled materials to protect them once they have formed a battery. One potential application is in very small devices. "It should be relatively easy to make a very small footprint device, rice-grain-size and smaller--the size of the head of a pin," Chiang says. He adds that self-assembly could allow more-efficient use of space than conventional batteries can. That's in part because it's possible for the electrode particles to pack into irregular shapes within a device or follow its outside contours. As the researchers move toward such applications, which could include use in distributed sensors for the military, their next step is to replace the liquid electrolyte with a solid polymer to make the battery more rugged. The better understanding of the relevant short-range forces could also be used to select different materials for applications in transistors or certain types of solar cells. [ permanent link to this entry ]
Making the right robot for the right job Link [Podcast: Web site for creating, sharing digital photo slide.] Thrun, who led the winning team in a robotic car race sponsored by the Pentagon in 2005, was one of four experts who spoke about the current and future state of robotics at the annual meeting of the American Association for the Advancement of Science. The association today wraps up a five-day event that attracted researchers from 60 countries to explore many fields including robotics. The term "robot" was coined in the 1920s when Czech playwright Karel Capek used the word "robota" -- relentless work or drudgery in his own tongue -- to describe a factory of mechanical creatures that eventually revolt. Deceased science fiction author Isaac Asimov popularized robots in the 1950s. The 1977 "Star Wars" movie made heroes of C-3PO and R2-D2. As Saturday's talks revealed, the convergence of key technologies hint that, within decades, robots may be able to perform tasks that were hitherto only fiction. These advances include: -- cheap, effective sensors that substitute for biological senses; -- sophisticated software and computers that approximate nerves and brains; and -- the ability to manufacture tiny mechanisms to mimic muscles. Thrun's robotic car is a prime example of the first two trends. His vehicle is a Volkswagen that is essentially the same as any driver-operated car. His task is to marry sensing systems placed atop the vehicle -- they resemble the lights on a police car -- with software being written by his Stanford collaborator Mike Montemerlo. The sensors include a bug-eyed camera that offers a 360-degree field of view and a novel device that uses light, instead of sound, to paint radar-like three-dimensional pictures of the roadway. The input from these and other sensors must be assembled and comprehended by software before the robo-car can act. Here, Thrun said in a briefing before Saturday's talk, human parents have a huge advantage when teaching teens to drive: Kids can discern the difference between a garbage pail and a pedestrian, whereas artificial intelligence systems must be trained to recognize and understand the object before they react by stopping or swerving. Thrun is currently working on a second-generation robo-car that will participate in another Pentagon-sponsored race in November -- this time trying to navigate city streets, possibly on a military base. At least Thrun didn't have to re-invent the wheel. But panelist Robert Full, a UC Berkeley biology professor, showed conferees Saturday how his lab is re-engineering the leg to design robots that can walk over rubble or climb walls. Full, who studies insects and animals as models for multi-legged machines, showed video of a vertical treadmill used to study how gecko lizards climb. Such studies have revealed that they use millions of microscopic hairs that grow on the surfaces of their toes to grasp the molecules of the wall. "They look like the worst case of split ends you could imagine,'' Full quipped. San Francisco State University professor David Calkins, looked the furthest ahead suggesting that robots would eventually become personal companions, answering questions, serving as butlers, even reading children bedtime stories. Calkins said life-like robots could be used in elder care, performing routine medical functions like dispensing pills in hospitals, and serving as home care providers. He hinted that robot companionship could one day go, as teens once said, all the way, for "geek bachelors who can't get a girlfriend." UC Berkeley engineering professor Ken Goldberg talked about using "smart" video cameras to search for proof that the ivory-billed woodpecker, a bird once thought extinct, may still exist in pockets of wooded swamplands in Arkansas. Using cameras to scan the skies, and software to sift through endless hours of video for flying birds that might be this sought-after creature, Goldberg said robotic vision systems might settle a debate that has divided birdwatchers. But Goldberg said the same automated technologies could be used to scan crowds on city streets. "There are big privacy implications in this," he said. In many ways today's robots remain as laughable as computers were 20 years ago. Full showed off a wall-crawling device called the StickyBot that had some trouble climbing the windows at the back of the meeting room. Full made a reference to a future in which mechanical arms and legs give people the sort of powers envisioned in the 1970s television series, "The Six Million Dollar Man." "People who were once thought to be disabled could have the possibility of being super beings," said Full, adding that while he isn't sure how society will deal with it, this issue is coming. [ permanent link to this entry ]
The Future of Sustainability Link [ permanent link to this entry ]
|
 |
