Stretchable battery for wearable gadgets

Researchers from Stanford University have developed a soft and stretchable battery for wearable electronics that relies on a special type of plastic to store power more safely than flammable material used in the conventional batteries today.

The adoption of wearable electronics has so far been limited by their need to derive power from bulky, rigid batteries that reduce comfort and may present safety hazards due to chemical leakage or combustion.

"Until now, we haven't had a power source that could stretch and bend the way our bodies do, so that we can design electronics that people can comfortably wear," said chemical engineer Zhenan Bao, who teamed up with materials scientist Yi Cui to develop the device.

For some time, lithium ion batteries have used polymers as electrolytes -- the energy source that transports negative ions to the battery's positive pole.

However, those polymer electrolytes have been flowable gels that could, in some cases, leak or burst into flame.

To avoid such risks, the Stanford researchers developed a polymer that is solid and stretchable rather than gooey and potentially leaky, and yet still carries an electric charge between the battery's poles.

In lab tests, the experimental battery maintained a constant power output even when squeezed, folded and stretched to nearly twice its original length.

The prototype is thumbnail-sized and stores roughly half as much energy, ounce for ounce, as a comparably sized conventional battery.

"One potential application for such a device would be to power stretchable sensors designed to stick to the skin to monitor heart rate and other vital signs," the researchers noted in the journal ature Communications.