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Stretchable batteries for flexible electronics could be used inside the human body

Yonggang Huang, of Northwestern University, and John A. Rogers, of the University of Illinois, have developed a stretchable lithium-ion battery. They contend that the stretchable batteries can power flexible electronic devices. The ultra-stretchy batteries could even be used to monitor brain waves and heart activity.

“An important trend in electronics involves the development of materials, mechanical designs and manufacturing strategies that enable the use of unconventional substrates, such as polymer films, metal foils, paper sheets or rubber slabs. The last possibility is particularly challenging because the systems must accommodate not only bending but also stretching. Although several approaches are available for the electronics, a persistent difficulty is in power supplies that have similar mechanical properties, to allow their co-integration with the electronics,” write the researchers in the journal Nature Communications.

Huang and Rogers have revealed a battery that continues to work even when stretched, folded and twisted. The battery lasts for approximately eight to nine hours and can be recharged wirelessly. The novel battery allows for true integration of electronics and power into a tiny, stretchable package.

“Here we introduce a set of materials and design concepts for a rechargeable lithium ion battery technology that exploits thin, low modulus silicone elastomers as substrates, with a segmented design in the active materials, and unusual ‘self-similar’ interconnect structures between them,” write the researchers.

According to Huang and Rogers, the power and voltage of the stretchable battery are similar to a conventional lithium-ion battery of the same size. However, the stretchable battery can stretch up to 300 percent of its original size and still work flawlessly.

Huang and Rogers have been reportedly working together for the last several years on flexible electronics. So far, designing a cordless power supply has been the biggest obstacle to their success. Now they have overcome the problem with their “space filling technique.”

Huang and Rogers developed “pop-up” technology that allows circuits to bend, stretch and twist. They developed an array of  small circuit elements connected by metal wire “pop-up bridges.” When the array is stretched, the wires pop up.

While this approach works for circuits, it is not suitable for stretchable batteries. They note that there is not enough space between battery components for the “pop-up” technology to work.

Huang solved this problem by using metal wire interconnects that are long, wavy lines, filling the small space between battery components. As the battery is stretched, the first line connecting the components stretches out and disappears. As the stretching continues, the smaller “S’s” within the large “S” shape of the line stretch out and disappear.

“We call this ordered unraveling,” Huang said. “And this is how we can produce a battery that stretches up to 300 percent of its original size.”

Huang and Rogers report that the battery is capable of 20 cycles of recharging with little loss in capacity. Details of the invention are published in the journal Nature Communications.

According to NBC News, Rogers was awarded the $500,000 Lemelson-MIT Prize in 2011. Rogers was chosen for his ability to translate his ideas into inventions and innovations.

Photo credit: Yonggang Huang