The lightweight reinforced resins used to make golf clubs, bicycle frames and airplane wings have one weakness: They develop invisible cracks and break without warning. Scott White, materials engineer at the University of Illinois at Urbana-Champaign (UIUC), wants to eliminate the expensive inspection and upkeep of these materials. Collaborating with UIUC materials scientist Nancy Sottos and chemist Jeff Moore, he’s created resins that heal themselves when damaged.
Two types of tiny capsules, like the separate cylinders in a tube of epoxy, are scattered throughout these “autonomic materials.” One contains a hardening agent, the other a trigger. The capsules rupture when cracks occur and their contents spill into the gap, where they mix, harden, and seal the fissure.
In 2008, White started Autonomic Materials, Inc. to commercialize the technology developed in his lab. The company sells customized self-healing paints and coatings for bridges, cars and boats.
At the February 2011 meeting of the American Association for the Advancement of Science in Washington, D.C., White talked about how self-healing materials can make lithium-ion batteries safer and longer lasting. SciCom’s Melissae Fellet caught up with him to learn why laptops burst into flames and how fully electric vehicles could become reality.
What is an autonomic material?
It’s a material that responds to some sort of stimulus, without human intervention, in an automatic fashion. It’s similar to biological systems.
So you cut it and it heals on its own. It knows what to do.
It knows what to do. You build it into the material. It completely works on its own.
What can we use them for?
I think the first commercial application we’ll see is self-healing coatings and paints. A couple years ago, Nissan announced that they have a self-healing paint for their car, which was a pretty early version of these kinds of things. I don’t know that I would classify it as self-healing yet, because you have to let it sit in the sun for about a week and heat up. But that kind of idea is certainly being undertaken by lots of companies right now.
What got you interested in it?
My forte is in composite materials for things like aircraft. [Composites consist of plastic resins reinforced with ribbons of fiberglass or carbon fiber.] They’re great materials. They can’t be beat. But their one downfall is that when they fail, they fail catastrophically, with little forewarning.
I had this outlandish idea that we could make a material inspired by the biological healing process. So a small group of us gathered around a table and just brainstormed. We threw out all kinds of wild ideas, some of which I think will never see the light of day. But one that we struck upon pretty quickly was the idea of microcapsules. I knew there was a possibility we could encapsulate what we want and disperse it in some kind of polymer matrix.
You’re talking at this meeting about lithium-ion batteries. How can we use this concept of autonomy for these batteries?
We’re integrating capsules that impart some sort of functionality to the battery, and we’re building those capsules into the battery fabrication process. There are two things we’re focused on. One is safety. The second is longevity.
"The [Chevy] Volt has pushed existing lithium-ion battery technology to the upper limits. A full electric vehicle is still way outside of the bounds."
There’s a lot of ways the battery can become unsafe. It could be a loose connection, overcharging, or excessive heat. Ultimately, a runaway chemical reaction occurs and the temperature of the battery spikes very high. When that happens, the battery cell will vent. Lithium is exposed to the atmosphere and it bursts into flames.
Exactly. There are well-documented battery fires all over the place. They don’t happen all that often, but when they do, the results are pretty severe.
So our approach to this was to build thermally responsive capsules into the battery. When some critical temperature is reached, these capsules will then release their payload. We essentially shut down ion conduction at that point. It kills the battery and prevents it from overheating and bursting into flames.
For the longevity problem, there are multiple degradation processes that begin the moment you turn it on and start to use it. One example is small cracks in the anode. With a crack, there’s no conductive pathway, and that leads to a whole host of other problems. Conductive particles are inside our capsules—nanotubes in one example, liquid metals in another. You release those and they restore conductivity.
Can these cracks form if I drop my computer?
Absolutely. In fact, impacting the battery is one way of setting off a fire. So don’t drop your battery.
Have you had any fires while you’re experimenting?
We try to prevent them [laughs]. One of the things we’re ramping up to do right now is what’s called an in situ overcharge and thermal runaway. That’s where you do things to purposefully set the battery on fire, like driving a nail through it. There’s a possibility that we’ll see fires then, but hopefully we’ve proved out the technology so we’re not going to see that happen.
I think if it was me, I would just shut the fume hood and run away.
We’ll have plenty of safety gear.
What makes lithium-ion batteries so great? Why are we stuck trying to fix them?
In terms of commercial systems, nothing outperforms lithium-ion batteries. They can’t be matched in terms of their portability and power. So for the foreseeable future, that’s what we’re using.
The [Chevy] Volt has pushed existing lithium-ion battery technology to the upper limits. A full electric vehicle is still way outside of the bounds. We can move the energy density up, theoretically by ten times, if we go to silicon anodes. But it cracks after a few cycles. If we can heal that or prevent it from occurring, then all of a sudden you can reach that full electric goal.
If you seal the cracks, you could extend battery life as well.
Exactly. Most people replace their laptop batteries within a couple years. But if you’re thinking about a hybrid car or electric car, we’re talking about much longer lifetimes. Right now we have to swap out car batteries. If we can extend their lifetime three- or four-fold, then we can think about having a single battery that lasts for ten years.
That’s a big challenge for battery technology. But it seems like people have been working on this for a while.
That’s what’s interesting about this meeting. The theme [at AAAS] this year was “Science Without Borders,” and the focus of the symposium was how bringing in ideas from other fields can lead to advancements in relatively old problems. A year and a half ago, our group had never looked at a battery. So you might think, “What am I talking about here?” But we applied the kinds of research we’d been doing for more than 15 years to a targeted problem. And it does translate.
Nancy Sottos has described the autonomic materials project as starting from the bottom-up. There was no book to follow—you wrote the book. How’d you keep going when it was frustrating?
Fundamentally, you have to believe in what you’re doing because you’re going to face all kinds of problems along the way. We started with this concept for autonomic healing polymers in 1995, and it was mid-to-late 2000 before we saw a single experiment that showed it was going to heal. So that’s five years of failure in a row. Ultimately, it did work out.
Now we take really tough, outlandish problems and we play. That’s where it’s fun, where there isn’t a book or a roadmap for you to follow. We’re very creative about how we approach these things. Some of them work, some of them don’t. But at least we’re out there trying.
It seems like it’s translated very quickly. The first experiment worked in late 2000, and now it’s 2011. You’ve started a company and you’re working in batteries now. It’s just exploded.
It’s been quite a ride, nothing I would have ever predicted. And we’re having a lot of fun. At the heart of this is the unique collaborative group we have. We’re all friends first and collaborators second. That makes it a lot of fun. You want to come in to work and do something.
What inspired you to start a company for these coatings?
Countless companies have come to Beckman [Institute at UIUC]. We walk them around the labs and talk about the technology and how it can be scaled in a plant. It was frustrating to see that years were going by and this work wasn’t really being translated to commercial products. We got funding and we were able to hire two of our former group members to stick around and start the company. It’s taken off from there.
Do you have plans to commercialize the lithium-ion battery technology you’re developing?
I would like to see everything we do applied in some way. We certainly have filed patents on the kind of technology that I’m talking about. If it proves to be as good as we’re seeing here, and it’s easily integrated, then I would expect to see it.
How long do you think that will take?
Every estimate I ever make has to be doubled. I think we’re looking at 5 to 10 years out, because it is so new. No matter how many experiments you prove out, everybody else is going to want to go through the same process of testing and evaluation.
Do other companies want to use the technology in their batteries?
They’re not aware of it yet. I’ve got the drafts of two papers on my desk that cover this. They’re not out to the public yet.
It seems like a lot of practical applications drive your work. If you could chase anything, what would it be?
Certainly energy is one. There are all kinds of issues in terms of collecting energy from alternative energy sources that don’t make the economics work out. But if we’re able to have autonomous materials in wind turbine blades that last much longer and are much lighter, that changes the scenario completely. We’re not working on that, but I would love to.
Health is another. For example, hip replacements have a 10-year lifetime. If you’re 20 years old and you have a hip replacement, you’re talking about many surgeries over your lifetime because the materials degrade in your body. If we can combat that problem, then we’re talking about one surgery.
In our January group meeting, I challenged everybody, “Let’s work on the really big problems.” If you don’t dream big, you’re certainly not going to solve these things.
Melissae Fellet, a 2011 graduate of the Science Communication Program at UC Santa Cruz, earned her bachelor’s degree in microbiology and biochemistry from the University of Florida and her Ph.D. in chemistry from Washington University in St. Louis. She has worked as a reporting intern at the Salinas Californian, KUSP-88.9 FM public radio in Santa Cruz, the Stanford University News Service, and New Scientist in San Francisco. She is now a freelance science and technology journalist, based in Santa Cruz.
© 2011 Melissae Fellet