Viruses build tiny batteries

MIT scientists have manipulated the genes in viruses to coax them to build nanowire structures for use in very thin lithium-ion batteries.

The goal of the work, led by MIT Professors Angela Belcher, Paula Hammond and Yet-Ming Chiang, is to create batteries that store as much electrical energy in 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.

The MIT team used an intricate assembly process to create the battery anode. They manipulated the genes in a laboratory strain of a common virus, making the microbes collect cobalt oxide and gold. Because these viruses are negatively charged, they can be trapped between oppositely charged polymers to form thin, flexible sheets. The resulting dense, virus-loaded film serves as an anode.

The MIT team then made the cobalt oxide and gold-coated viruses align themselves on the polymer surface to form ultrathin wires. Each virus, and thus the wire, is only 6 nanometres in diameter, and 880 nanometres in length.

“For the metal oxide we chose cobalt oxide because it has very good specific capacity, which will produce batteries with high energy density,” said Belcher. This means it can store two or three times more energy for its size and weight compared to previously used battery electrode materials. Adding the gold further increased the wires’ energy density.

Equally important, the reactions needed to create nanowires occur at normal room temperatures and pressures, so there is no need for expensive pressure-cooking technology to get the job done.

The research is important as it could mean batteries with a much greater energy density in the future. The team said the nanoscale materials they made supply two to three times the electrical energy for their mass or volume, compared to previous materials.