Tuesday, April 7, 2009

Virus help make 'green' batteries

Researchers tap viruses for 'green' batteries

Posted:07 Apr 2009

Massachusetts Institute of Technology (MIT) researchers claim that viruses can be used to assemble tiny batteries that can then be printed on plastic films.

The MIT investigators reported details April 2 of genetically-engineered viruses that were used to self-assemble nanoscale Li-ion battery materials. The resulting batteries were then printed onto plastic films using green processes.

MIT researchers claimed to have perfected the last major component of its flexible battery film, demonstrating performance comparable to existing Li-ion batteries that run everything from laptop computers to hybrid automobiles. The team is currently optimizing its materials to boost performance beyond existing Li-ion batteries. Eventually, they plan to commercialize the printable battery films.

"Viruses offer a new way of wiring batteries," said team leader Angela Belcher, a MIT materials scientist. "Now we have the anode material, the cathode material and the micro-contact printing method." Next, they must "stamp out whole batteries, optimize their performance and scale up the technique for commercialization."

Along with boosting battery performance, the MIT scientists said they will adopt form factors impossible today by using inexpensive, printable assembly techniques. For their demonstration, the MIT researchers fabricated a typical coin-cell battery.

Last week, MIT president Susan Hockfield demonstrated the prototype battery to U.S. President Barack Obama. During a White House briefing on green energy technologies, Hockfield said flexible battery films could be manufactured near room temperature using environmentally benign processes.

A typical Li-ion battery uses a negatively-charged anode made of graphite to regulate the flow of lithium ions to the positively-charged cathode, which is made of cobalt. In MIT's version, the anode and cathode materials are self-assembled into structures that provide more surface area due to the nanoscale patterning of living viruses. The viruses were selected from among populations of common bacteriophages, which infect bacteria but are harmless to humans.

MIT's Angela Belcher lead the printed battery research team.

Genetically-engineered viruses
The researchers genetically engineered the viruses to self-assemble nanoscale battery films by creating billions of random variations, then using the survival-of-the-fittest principle to select those that best performed desired tasks.

Last year, the team demonstrated the ability to use micro-contact printing techniques to fabricate flexible battery films from anode materials that were self-assembled by viruses. The demonstration used a traditional cathode material.

Genetically-engineered viruses can now also self-assemble nanoscale cathode material, providing the final component necessary for commercialization.

"We have used genetic engineering to grow a cathode material—nanowires of lithium ion phosphate plus silver, which then pickup a single carbon nanotube at their tip to increase their conductivity," said Belcher.

MIT's previously demonstrated self-assembly of the anode material using a different virus that coats itself with cobalt oxide and gold to form a nanowire. The new virus harnesses a similar method to coat itself with iron phosphate and silver, then uses molecular recognition to pick up nanotubes on their ends for more efficient electron transport.

"We first tried to engineer the material without the nanotubes, but its conductivity was not good enough. So we found a virus that would attach to nanotubes by virtue of molecular recognition," said Belcher. "That was the hardest part, since only two out of a billion viruses—each with a different genetic code and selected by the survival-of-the-fittest principle—picked up a nanotube on its tip."

The resulting material—which can be mass produced in solution, then dried into a powder—consists of about 5 percent carbon nanotubes. In demonstrations, batteries stamped out using the micro-contact printing method were able to be recharged hundreds of times with no detectable drop in performance.

The MIT researchers next hope to refine their lithium-based material formulations to provide even better performance by adding metals to their lithium phosphate mix, including lithium magnenese phosphate or lithium nickel phosphate.

Funding for the MIT research was provided by the U.S. Army Research Office Institute and the National Science Foundation through its Materials Research Science and Engineering Centers program.

- R. Colin Johnson
EE Times

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