Stretchable battery to power implants inside the human body

Scientists at the Northwestern University have demonstrated a rechargeable lithium-ion battery that can be stretched, twisted and bended, and still capable of powering electronics.
The power and voltage of the stretchable battery are similar to a conventional lithium-ion battery of the same size, but the flexible battery is able to succeed where flat, rigid batteries would fail.
The revolutionary battery can be used anywhere, including the inside of the human body. It can stretch up to 300 percent of its original size and still function. It will power a commercial light-emitting diode (LED) for eight to nine hours – even when stretched, folded, twisted and mounted on a human elbow – before it needs recharging, which can be done wirelessly.

Yonggang Huang (Northwestern University) and John A. Rogers (University of Illinois) are the first to demonstrate a stretchable, implantable lithium-ion battery which could power implantable electronics that monitor brain waves or heart activity. Huang and Rogers have been working together for the last six years on stretchable electronics, and designing a cordless power supply has been a major challenge. Now they have solved the problem with their clever “space filling technique,” which delivers a small, high-powered battery.
For their stretchable electronic circuits, the two developed “pop-up” technology that allows circuits to bend, stretch and twist. They created an array of tiny circuit elements connected by metal wire “pop-up bridges.” When the array is stretched, the wires — not the rigid circuits — pop up. This approach works for circuits but not for a stretchable battery. A lot of space is needed in between components for the “pop-up” interconnect to work. Circuits can be spaced out enough in an array, but battery components must be packed tightly to produce a powerful but small battery. There is not enough space between battery components for the “pop-up” technology to work.
Huang’s design solution is to use metal wire interconnects that are long, wavy lines, filling the small space between battery components. (The power travels through the interconnects.)