Portland, Ore. -- Battery technology has historically lagged far behind semiconductor technology. While chips double their capacity every 18 months or so, batteries are lucky to double capacities in a decade.
But now, say materials scientists at the Massachusetts Institute of Technology, bioengineering has broken the bottleneck. Almost half the materials in today's batteries do not contribute to electricity storage, whereas MIT's bioengineered batteries aim to put more than 90 percent of their materials to work storing energy. To do that, the scientists--professors Angela Belcher, Paula Hammond and Yet-Ming Chiang--employ genetically engineered living viruses to assemble thin-film nanowires as the anodes and cathodes of a flexible "battery wrap." At 100 nanometers thick, the next-generation battery wrap can conform to any shape, they said.
"We are using biology to template electrode materials and have them self-assemble into structures for batteries," said Belcher. "These batteries are like Saran wrap--they are thin, flexible and can be bent into any shape, making them good for lightweight conformable applications."
The battery wrap invented at MIT is based on a genetically engineered derivative of the M13 bacteriophage--a virus parasite that infects a bacterium and reproduces inside it. By altering the genetic dispositions of this well-understood laboratory virus, which cannot infect humans, the materials scientists have been able to persuade the virus to extract cobalt-oxide and gold ions from solution and assemble them into a monolayer of nanowires functioning as a battery anode atop a polyelectrolyte substrate.
"M13 is a virus that has very specific host bacteria," said Belcher. "But our lab has had quite a few years' experience genetically altering this organism to grow many different types of materials. This time we took particular advantage of the very beautiful coat structure of M13 bacteriophage by engineering it to do three things: first, to grow cobalt-oxide nanowires; second, to create a hybrid electrode that is a combination of cobalt-oxide and gold within a single wire, making it a good ionic conductor as well as a good electronic conductor; and, finally, we got it to self-assemble on the polyelectrolyte of our battery in a monolayer structure."
The MIT researchers demonstrated prototype batteries with a virus-assembled anode. A traditional lithium cathode provided the other electrode. The team altered the virus' genes in a way that caused their protein coats to collect molecules of cobalt-oxide and gold. The viruses aligned themselves on a prepatterned scaffold, forming parallel wires the same width and length as the viruses: 6 x 880 nanometers.
The researchers plan next to re-engineer a version of M13 to grow the lithium cathode on the other side of the polyelectrolyte substrate. After that step, which may take several years to perfect, the scientists hope to market their battery wrap commercially. Belcher has already founded one successful MIT spin-off, Cambrios Technolo-gies Corp. (Mountain View, Calif.), whose work on biomorphic nanostructures received the 2006 EE Times Annual Creativity in Electronics (ACE) award for "Most Promising Technology" (see April 10, page 21).