Lithium-ion batteries are notoriously inflexible, but a new study created one using hydrogels that can survive a surprising amount of punishment.
According to researchers at UC Berkeley, the battery can even be cut in half, and still retain roughly 90 percent of its original capacity after self-healing.
While a good fit for technologies like wearables and soft robotics, it’ll still be awhile before these batteries compete in energy density with their more rigid competition.
Lithium-ion batteries are not known for their flexibility or rugged durability, and if you push these batteries too far, you end up with an explosive, toxic, and all-around chaotic mess. But as technology continues to proliferate into every corner of our lives, we’ll eventually need to overcome these physical engineering limitations.
For years, scientists have been working on ways to make a battery capable of twisting, stretching, and even sustain severe damage. Although nowhere near as energy dense or reliable as the lithium-ion battery in your smartphone, researchers around the world have made some serious progress with several different potential solutions. Now, a new study from a team of scientists led by the University of California Berkeley—published in the journal Science Advances—describes what may be the best flexible battery yet.
The key to this breakthrough was making a water-scarce hydrogel electrolyte paired with fluorine-free lithium salts. This wasn’t easy, as these are not the typical ingredients found in your run-of-the-mill lithium-ion battery. But by going this route, the team was able to develop a battery that could remain stable at higher voltages while not relying on toxic fluorine compounds. Of course, creating such a battery essentially from scratch wasn’t easy.
“Many materials we used are nonstandard to conventional lithium-ion batteries,” Peisheng He, a postdoctoral researcher from UC Berkeley and the lead author of the study, told IEEE Spectrum. “We surmounted those challenges by learning lessons from unsuccessful trials, building and constantly improving fabrication and testing protocols.”
Operate a higher voltage? Check. Non-toxic? Also check. But the real advantage of this battery is its unprecedented flexibility. Stretchable batteries themselves aren’t new—in fact, earlier this month, a team at Linköping University in Sweden revealed a stretchable battery somewhat similar to the texture of toothpaste that could handle 0.9 volts and recharge some 500 times.
This new battery, however, can not only handle more than triple that voltage while surviving tortuous twisting, folding, stretching, and hammering—it can also be stabbed repeatedly and still supply power. To take it even one step further, the researchers cut the battery completely in half, and after the battery self-healed, it retained up to 90 percent of its original capacity.
While this is marked improvement over previous attempts—previous flexible battery iterations only remained stable at 1.23 volts, for example—the energy density is roughly one-tenth that of a traditional lithium-ion battery. However, future improvements via electrolyte chemistry and electrode structure could eventually bring a big energy boost to everything from soft robotics to smartwatches.
“Integrating our batteries into the wristband of a smartwatch can multiply the watch’s battery capacity, such that one may only need the recharge once a week or longer,” Anju Toor, a co-author of the study from Georgia Institute of Technology, said to IEEE Spectrum.
If technology is the future, then flexible, self-healing batteries will likely be the energy source powering that future.
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