MIT scientists have harnessed the construction talents of tiny viruses to build ultra-small "nanowire" structures for use in very thin lithium-ion batteries. By manipulating a few genes inside these viruses, the team was able to coax the organisms to grow and self-assemble into a functional electronic device.
The goal of the work, led by MIT Professors Angela Belcher, Paula Hammond and Yet-Ming Chiang, is to create batteries that cram as much electrical energy into as small or lightweight a package as possible. The batteries they hope to build could range from the size of a grain of rice up to the size of existing hearing aid batteries.
Batteries consist of two electrodes - an anode and cathode - separated by an electrolyte. In the current work, the MIT team used an intricate assembly process to create the anode.
Specifically, they manipulated the genes in a laboratory strain of a common virus, making the microbes collect exotic materials - cobalt oxide and gold. Because these viruses are negatively charged, they can be layered between oppositely charged polymers to form thin, flexible sheets. What results is a dense, virus-loaded film that serves as an anode. A report on this work appears in the April 7 issue of Science.
In their research, the MIT team altered the virus's genes so they make protein coats that collect molecules of cobalt oxide plus gold. The viruses then align themselves on the polymer surface to form ultrathin wires. Each virus, and thus the wire, is only 6 nanometers (nm) in diameter, and 880 nm in length.
“We can make them in larger diameters,” Belcher said, “but they are all 880 nm in length,” which matches the length of the individual virus particles. And, “once we've altered the genes of the virus to grow the electrode material, we can easily clone millions of identical copies of the virus to use in assembling our batteries.”
“The nanoscale materials we've made supply two to three times the electrical energy for their mass or volume, compared to previous materials,” the team reported.
The researchers' work was spurred by “growing evidence that ‘nanostructured’ materials can improve the electrochemical properties of lithium-ion batteries,” compared to more conventional batteries based on older technologies, the team wrote in Science.
But to create new battery materials, Belcher noted, special control is needed so just the right amounts of the exotic materials end up exactly where they belong. For more information, see http://web.mit.edu/newsoffice/2006/virus-battery.html