Thursday, September 28, 2006

Powerful Batteries That Assemble Themselves

MIT researchers are developing low-cost manufacturing methods based on the rapid reproduction of viruses. Angela Belcher, a panelist at the Emerging Technology Conference, explains.

By Kevin Bullis

Biology may be the key to producing light-weight, inexpensive, and high-performance batteries that could transform military uniforms into power sources and, eventually, improve electric and hybrid vehicles.

Angela Belcher, an MIT professor of biological engineering and materials science, and two colleagues, materials science professor Yet-Ming Chiang and chemical engineering professor Paula Hammond, have engineered viruses to assemble battery components that can store three times as much energy as traditional materials by packing highly ordered materials into a very small space.

Through a combination of genetic design and directed evolution, Belcher has created viruses that coat themselves with inorganic materials they wouldn't touch in nature, forming crystalline materials, which are doped at regular intervals with gold to enhance their conductivity. Then the coated viruses line up on top of a polymer sheet that serves as the electrolyte, to form one of the battery's electrodes (see "Virus-Assembled Batteries"). The device looks like a thin sheet of cellophane.

Now Belcher is engineering viruses to assemble the second electrode, with the goal of creating an extremely compact, self-assembled battery.

We sat down with Belcher, who is presenting her work today at Technology Review's Emerging Technologies Conference, to learn how the work is progressing.

Technology Review: What are the limitations of current batteries and battery-manufacturing methods?

Angela Belcher: One of the problems with how batteries are made is there is a large component of the battery that's not active material. What we're looking at doing is using organisms to engineer the battery so that most of the battery is active material, so there's not a lot of wasted space and wasted weight. Viruses are engineered to sit directly on the electrolyte and grow the materials.

Something we're really interested in, too, is environmentally friendly approaches. In all the processes that we use to grow materials we try to make it so there's not a lot of waste product around. We don't use any organic solvents--everything's done in water. And the biology fine-tunes the process so you can build all your particles the way you want them to be built--you don't have to separate out the ones you don't want. When you actually go to dispose of the battery, there's much less, because it's much smaller. And a good fraction of it is actually biological, so it will degrade naturally.

TR: This could be a very low-cost approach to making batteries?

AB: Yes. It seems low cost when you are only making a couple--we don't know how that will scale yet.

TR: When we last talked, you had made an electrode of cobalt oxide, and there were plans to move forward into other materials.

AB: Right now we're working on [making] the other electrode out of lithium iron phosphate. Because we can evolve our system to work with lots of different kinds of materials, we're looking at other kinds of metal oxides. But right now we're just trying to focus on the two: the lithium iron phosphate, which will also have gold with it, and also the cobalt oxide with gold.

TR: Did you choose lithium iron phosphate, rather than materials typically used now in lithium ion batteries, for safety reasons? (See "Safer Lithium-Ion Batteries".)

AB: It's partly for safety concerns, and it's also a material that is not hard to think about how to make it [with] biological synthesis. Biology processes phosphates very easily, for instance, in bone. And it also processes iron easily. So iron phosphate is a good choice.