Medical News
Robots like this one could benefit from stretchy batteriesMASSIMO BREGA, THE LIGHTHOUSE/SCIENCE PHOTO LIBRARY
By Donna LuWearable devices could soon be more flexible – in future they might be powered by stretchable batteries.
Nicholas Kotov at the University of Michigan and his colleagues have developed a conducting component for a lithium-ion battery that maintains its electrical conductivity even when stretched to a strain of more than 300 per cent.
The conductor is made from multiple layers of polyurethane and gold nanoparticles. Polyurethane is a polymer used to make common objects such as foam sponges and garden hoses.
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Layers of negatively charged nanoparticles are alternated with positively charged layers of the softer polymer. As the conductor is stretched, the gold nanoparticles self-organise into aligned pathways, allowing them to continue conducting electricity.
Stretchiness versus conductivity
A major challenge of designing flexible batteries is finding a balance between stretchiness and electrical conductivity, says Kotov.
The team tested the performance of the conductor in a battery with a lithium electrolyte. The stretchable battery has a lower power density than regular lithium ion batteries, but after 1000 cycles, it retained 96 per cent of its capacity. This dropped significantly in tests in which the battery was always in its stretched state: under those conditions it retained only 72 per cent of its capacity after just 10 cycles. But once the strain is released, its capacity increases again.
Kotov envisages such batteries could be used in wearable or implantable devices, as well as used in soft robots with flexible legs or tentacles.
He says the properties of the battery can be modified. “We can adapt to the specific mechanics and charge storage requirements that implantable devices or other devices might need,” he says.
Journal reference: Science Advances, DOI: 10.1126/sciadv.aaw1879