Flexible battery completes stretchable electronics package

February 28, 2013

Operation of the lithium-ion battery connected to a red LED while biaxially stretched to approximately 300 percent (credit: Sheng Xu et al./Nature Communications)

Northwestern University scientists have demonstrated the first stretchable lithium-ion battery — a flexible device capable of powering innovative stretchable electronics.

This development makes it now possible that these stretchable electronic devices could be used anywhere, including inside the human body.

The implantable electronics could monitor anything from brain waves to heart activity, succeeding where flat, rigid batteries would fail.

The battery can work for eight to nine hours before it needs recharging, which can be done wirelessly, enabling integration of electronics and power into a small, stretchable package.

The power and voltage of the stretchable battery are similar to a conventional lithium-ion battery of the same size, but the flexible battery can stretch up to 300 percent of its original size and still function.

How it works

Electrode pads and interconnects of the lithium-ion battery (credit: Nature Communications)

Tightly packed, long wavy wires provide the flexibility, filling the small space between battery components, says Yonggang Huang, the Joseph Cummings Professor of Civil and Environmental Engineering and Mechanical Engineering at Northwestern’s McCormick School of Engineering and Applied Science. “When we stretch the battery, the wavy interconnecting lines unfurl, much like yarn unspooling.”

The unique mechanism is a “spring within a spring”: The line connecting the components is a large “S” shape and within that “S” are many smaller “S’s.” When the battery is stretched, the large “S” first stretches out and disappears, leaving a line of small squiggles. The stretching continues, with the small squiggles disappearing as the interconnect between electrodes becomes taut.

“We call this ordered unraveling,” Huang said.

Completed lithium-ion battery, in a state of stretching and bending (credit: Nature Communications)

The battery’s design allows for the integration of stretchable, inductive coils to enable charging through an external source but without the need for a physical connection.

The battery is capable of 20 cycles of recharging with little loss in capacity. The system consists of a square array of 100 electrode disks, electrically connected in parallel.

The research was supported by the Initiative for Sustainability and Energy at Northwestern University (ISEN).