Researchers create lithium-ion battery that can stretch to 300% its original size

Researchers at Northwestern and the University of Illinois at Urbana-Champaign have created a stretchable, flexible lithium-ion battery that can be recharged wirelessly. This is big news for wearable computing, roll-up displays, and implantable devices -- all of which have been desperately awaiting a flexible, stretchy power source.

Historically, batteries, with electrodes made out of large slabs of graphite and metal, are about as inflexible as it gets. Bend a laptop battery and, if you're strong enough, it will break (and possibly explode, so please don't try it at home). There's also a toxic, liquid electrolyte in most batteries, which generally means you want a hard, rugged chassis to stop any leakages.

This new stretchy battery, however, is made up of hundreds of tiny cells, connected by wires, on a stretchy silicone substrate. As you can see in the diagram above, the cells themselves are basically standard lithium-ion cells, packed within a protective silicone sheath. The wires, however, are fairly magical. Dubbed "a spring within a spring," (pictured below) the wires gracefully stretch but never become taut, even when the battery is stretched to three times its original size. "We call this ordered unraveling," says Yonggang Huang of Northwestern University. When tension and flexion are relaxed, the battery returns to its original shape and size.

In testing, the researchers built a one-inch-square battery with 100 individual cells. As you can see in the image at the top of the story, the battery continues to power the LED even when being very dramatically stretched. The researchers say that the battery withstood 20 charge/discharge cycles with little loss in capacity, but that "additional development efforts to improve the lifetime will be required for commercialisation."

Moving forward, this is definitely a significant advance for wearable and flexible computing -- imagine a battery that can sit against your leg or stomach and flex with your movements. The power density of this new, stretchy battery isn't very high -- but with a little work, it could be enough to power a handful of sensors and a small computer. When combined with some other recent developments, such as flexible displays, speakers, and circuitry, we are getting very close indeed to a truly wearable computer.

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