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UT research leads to revolutionary ‘self-healing’ gel for electronics

In the scramble to invent the battery of the future, many of the world’s brightest minds have focused on finding new materials for the parts that conduct the juice. Guihua Yu and his University of Texas research team focused on goo: a “self-healing” gel that could hold together the electrodes that tend to crack in next-generation batteries as they charge.

They got the gel to work late last year, according to a pair of peer-reviewed reports published in the scientific journal Nano Letters. The breakthrough has implications for technologies as small as an iPhone, as large as batteries that could power entire cities and as hip as Tesla’s electric cars.

It will be years before the gel is on the market, but the potential uses illustrate just how many sci-fi-sounding ideas are nearly a reality, thanks in part to advances in the “flexible electronics” field: phone batteries that could fix themselves; workout shirts with “biosensors” that could monitor someone’s heart rate; even, as a KUT report on Yu’s work noted, robots that could heal themselves when damaged. (Cue the T-1000 from “Terminator 2.”)

“This first step was demonstrating its properties,” Yu, who was named one of the top 35 innovators under age 35 in 2014 by MIT Technology Review, told the American-Statesman.

Make or break

The core problem that Yu’s team took on is that, generally speaking, various electronic components don’t bend well, if at all. If bent, they often break.

Yu’s team, rather than looking for ways to make the component itself more flexible, searched for a way for the component to bind itself back together the moment it breaks – making it essentially flexible. Earlier research several years ago at Stanford University, where Yu did postdoctoral work, led to a gel that could be applied to electrodes, one of the breakable components. When the electrodes broke, the gel could adhere the pieces together and keep the electricity flowing.

In theory, this would open the way for all sorts of advances in the electronics field. The problem was that those gels required a catalyst, such as intense heat or light, to trigger the healing process, so there has been little commercial use for them.

Yu’s team, though, engineered a gel that can activate on its own, without applying some external force to it. Thus, the “self-healing” part.

But adding the self-healing property required some complex chemistry and meant revisiting the core challenge: the strength of the chemical bonds that hold the molecules in the gel together. Too tight and they are too rigid and basically become part of the problem. Too loose and the molecules don’t hold together adequately and don’t keep the electronic component together when they break. They found a Goldilocks solution, not too tight or too loose, according to the Nano Letters papers.

“As a material chemist, that is something I’m particularly proud of,” said Yu, who came to UT in 2012.

The gel is still too expensive to mass-produce, and someone has to figure out how to apply it. Do they paint it onto a component, or dip the component into a dish of it? Do they apply it during the manufacturing process, or simply when something seems to have broken?

Yu envisions many potential uses for the gel. He is now talking with UT colleagues about ways the gel could be used in concert with flexible electronics. That field focuses on creating materials that are more bendy and stretchy.

Such technology has already been deployed as a patch, made from materials as soft and stretchy as skin, that can be applied to someone’s epidermis and monitor vital functions like blood pressure, said Nanshu Lu, a UT researcher who specializes in flexible electronics.

Another idea in the works, she said: “a subconscious interface” that can control prosthetic limbs. In that case, a patch would detect if, say, a chest muscle moves and convey a signal that would move a prosthetic arm.

The Defense Department announced in August that it will spend $75 million over five years on a hub in Silicon Valley to manufacture “flexible hybrid electronics.”

First applications

One of the central paradoxes in flexible electronics is that inflexible materials such as metals tend to be far better at conducting electricity than their more flexible counterparts, thus hindering attempts to make some kinds of devices more bendy, said Lu, an assistant professor in UT’s Department of Aerospace Engineering and Engineering Mechanics.

“Batteries, in particular, are more difficult to make flexible,” Lu said.

That is where Yu, whose expertise is in battery research, sees the first application of the gel.

Flexibility is important in next-generation batteries with ultrahigh capacity electrodes, he said, because they expand when charged. Despite attempts to make them withstand quite a bit, they can swell to the point of cracking, which causes immediate battery failure. Fear of cracking limits how full a battery can be stuffed and shortens the life of the battery. But one held together by self-healing gel could both store more energy and last longer, Yu said.

His goal, like many researchers, is to create batteries efficient enough to store enough energy to power cities. Batteries are not advanced enough now to make such large-scale storage cost-effective. Thus, communities cannot rely entirely on solar or wind power, which is not always consistent, and most rely on coal or natural gas plants, which can be run around the clock but produce carbon emissions that most climate scientists say contribute to global climate change.

Better technology might even allow all of that storage to happen inside electric-car batteries, which many futurists envision powering homes, as well.

“I think the gel can be part of this revolution,” Yu said.

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