Electronics are showing up everywhere: on our laps, in our pockets and purses and, increasingly, snuggled up against our skin or sewed into our clothing. But 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.
Stanford researchers have developed a soft and stretchable battery that relies on a special type of plastic to store power more safely than the flammable formulations used in conventional batteries today. The new stretchable battery was described recently in Nature Communications.
The use of plastics, or polymers, in batteries is not new. For some time, lithium-ion batteries have used polymers as electrolytes — the chemical medium that transports negative ions to the battery’s positive pole. But those polymer electrolytes are flowable gels that could, in some cases, leak or burst into flame.
To avoid such risks, the new polymer is solid and stretchable rather than gooey and potentially leaky. Yet it still efficiently 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 stores roughly half as much energy, ounce for ounce, as a comparably sized conventional battery.
The team is now working to increase the stretchable battery’s energy density, build larger versions of the device and run future experiments to demonstrate its performance outside the lab. 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 as part of the BodyNet wearable technology also being developed at Stanford.