Ellen Phiddian
Cosmos science journalist
Two teams of scientists have announced they’ve made stretchy, jelly-like batteries.
Flexible electronics, for things like health monitors, need flexible power sources. At the moment, this mostly means batteries made from tiny, rigid components.
These batteries, which are made with very different methods, are both stretchy all the way down. They represent 2 possible paths to more widespread flexible electronics.
One battery, made by a team of Chinese researchers, is a lithium-ion battery made from polymers.
The thumb-sized battery can expand to 50 times its original size, and retained its capacity after 67 charge and discharge cycles.
The researchers, who are based at Nanjing University of Posts and Telecommunications, made the battery by “printing” thin layers of ingredients onto a plate.
These layers included nanometre-sized silver wires, lithium salts for the anode and cathode of the battery, a coal-like pure carbon substance called carbon black, and the precursors for polymers like polydimethylsiloxane, which is used widely in medical and cosmetic products.
The researchers used light to treat this mixture, which solidified into a rubbery battery. Then, they coated it with an electrode film and a protective seal.
Testing shows that this all-solid, stretchy battery has “excellent” characteristics, according to the researchers’ paper, which is published in ACS Energy Letters.
“Undoubtedly, this work can further promote the development of stretchable energy devices for wearable/implantable electronics,” write the researchers.
The second battery, made by UK researchers, uses a different approach: instead of all-solid materials, it’s made from a hydrogel composed of water in a network of polymers.
The researchers at the University of Cambridge, say their jelly battery is self-healing and can stretch to 15 times its original size.
“It’s difficult to design a material that is both highly stretchable and highly conductive, since those two properties are normally at odds with one another,” says first author Stephen O’Neill, a PhD student at Cambridge’s Yusuf Hamied Department of Chemistry and first author on a paper published in Science Advances.
“Typically, conductivity decreases when a material is stretched.”
The researchers solved this problem by developing polymers that were ionic: they could hold electric charges. These polymers were used to build hydrogel layers.
“Normally, hydrogels are made of polymers that have a neutral charge, but if we charge them, they can become conductive,” says co-author Dr Jade McCune, also a chemist at Cambridge.
“And by changing the salt component of each gel, we can make them sticky and squish them together in multiple layers, so we can build up a larger energy potential.”
The hydrogel batteries can also survive being squashed to a tenth of their size, and repair themselves in under 30 seconds when damaged.
The researchers are planning animal trials to see how the hydrogels could work in medical devices.
“We can customise the mechanical properties of the hydrogels so they match human tissue,” says senior author Professor Oren Scherman, Director of the Melville Laboratory for Polymer Synthesis at Cambridge.
“Since they contain no rigid components such as metal, a hydrogel implant would be much less likely to be rejected by the body or cause the build-up of scar tissue.”
