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.
TR: People are looking at different organisms to try to create bioengineered materials, like sponges, diatoms, or abalone shells. Why did you choose viruses?
AB: Well, for a couple of reasons. What a lot of people think is interesting about biological materials is looking at the final structure. I did my PhD [work] on that and I think it’s a very interesting question. But that’s only going to get you so far. It will get you to understand how to make a diatom, or something very similar to a diatom.
To me, [what is] more interesting is that when an abalone makes offspring, it makes millions and millions of offspring that have the genetic information to build a beautiful shell. Wouldn’t it be great to be able to pass on genetically the ability to make a material, in this case battery material, solar cells, or all kinds of other things we’re working on? If you’re going to genetically manipulate a sponge or an abalone to change their offspring, it’s going to take a really long time, and it’s going to be very complex. Viruses are very easy to work with. They’re only DNA and protein. You don’t have to worry about messing up all kinds of other metabolic processes, and you can make millions of copies in a very short amount of time.
TR: But these other organisms already work with inorganic material. With viruses you don’t have that. Would you explain how you’re able to get them to assemble these materials?
AB: It’s actually borrowed from the idea of how those other organisms make materials, being able to grab onto ions out of solution and position them to make bonds and materials.
We’ve done a lot of experiments, so we know the kinds of amino acids that are good at binding different materials. For the cobalt oxide material, all we had to do was bind cobalt, and to do that, we used high concentrations of carboxylic acid proteins. The gold part we did through selection [creating millions of variations, and isolating the DNA of virus proteins that bind well to gold]. Then [we] put the DNA sequence that is good at capturing cobalt into the genome of the virus, with the sequence [for gold] in a different part.
TR: You’ve said before that you hope to be able to simply mix together precursors and viruses and then pull a complete device out of a beaker. How is that going?
AB: We’re definitely heading in that direction. We’re working very hard on being able to make the other electrode material. We expect to be there in another couple of months. In that case we’ll have the two electrodes and the electrolyte. We could probably think of doing something similar for the collector. So I don’t think it’s a complete fantasy. I think we’ll be able to do that in a short time, like within a year.
TR: Where will we see these batteries first?
AB: We’re working on spinning them into fibers for textile-integrated materials that would be inexpensive. We have ideas of how to make transparent stick-on batteries that look like Band-Aids. People are also interested in applications like smart cards, and I think that that’s definitely a possibility. Things that are really lightweight, cheap, and both rechargeable and disposable.
TR: Do you see applications in transportation?
AB: I’m having companies come talk to me about that. I don’t see how to scale it yet, because mostly we focus on making things very, very small. But I definitely don’t see it out of the realm of possibility at all, because for hybrid cars and so on, you’re going to want to have light-weight batteries.