About a month ago, we covered some impressive lithium battery tech. Researchers have developed a specific formulation of lithium-iron phosphate that allows lithium charges to rapidly move in and out of the storage medium, which allows for extremely fast charge/discharge cycles. Charges in this material move so quickly, in fact, that the primary limit to these batteries becomes the amount of electrode material needed to keep them fed. A potential way forward was released in Thursday's edition of Science Express: building highly structured electrodes using an engineered virus.

The fast-charge batteries were developed at MIT, and there is another group on campus that has been experimenting with using viruses to structure battery components (we've also covered some of their work in the past). The two teams have apparently been talking—one of the authors of last month's paper appears on the current one—and the new report involves using viruses to structure an electrode material that incorporates iron phosphate.

The basic concept that drives the work is the recognition that biological systems can self-assemble into ordered structures and, with the appropriate modifications, can be used to order additional materials. In this case, the biological material involved is the M13 phage, which assembles into long, filamentous structures using many copies of a few simple proteins. By altering the sequence of the proteins, it's possible to create viruses that have an affinity for a variety of materials.

In this case, the authors started with a modified virus, where a protein that forms the sides of the filament has an affinity for iron phosphate. By combining the virus/iron phosphate mix with a coating of conductive silver, the authors were able to use it as an anode in a standard lithium battery. This combination performed reasonably well, but not as well as existing commercial solutions, so the authors went back to the drawing board.

They concluded that, although the virus created useful structures on the fine scale, the resulting material lacked a larger-scale organization that would help increase the electric contacts in the battery. To provide this, the authors turned to another material that's been making waves in the world of nanotechnology: carbon nanotubes.

To build a higher order structure with carbon nanotubes, they had to link the virus up to them. So they selected a protein that resides at one end of the viral filament, randomly mutated it, and then screened for versions that stuck to nanotubes. They got several, and focused on two that had different affinities for the nanotubes; these differences allowed them to determine how important the virus-nanotube interactions were for battery performance.

Using a mixture in which the carbon nanotubes contributed only five percent of the mass increased the performance of the batteries by about 20 percent, and provided even larger improvements at higher discharge rates. The new electrode also tripled the energy density compared to one made with a normal virus. A form of the virus with lower affinity for the nanotubes produced an intermediate value, showing that the interactions were essential for this improved performance. In all cases, the material showed very little change in capacity after multiple recharge cycles.

The authors were able to demonstrate a functional 3V battery that is able to power a small LED, as shown above.

As far as I can tell, this new development is complementary with the fast-charge technology described last month; that paper focused on the charge storage material, while this involved a new electrode structure. So, it should be possible to combine the two approaches. Given that the labs involved appear to be collaborating, I'd be surprised if work in that area isn't already underway.

Science, 2009. DOI: 10.1126/science.1171541

Listing image by Yung Jun Lee and Dong Soo Yung