April 25, 2017 feature
Stretchable sodium-ion battery electrodes made using sugar cubes
The scientists, led by Guihua Yu at the University of Texas at Austin, have published a paper on the new stretchable batteries in a recent issue of Advanced Materials.
By starting with sugar cubes, the researchers were able to obtain the size, shape, and porosity needed for high-performance battery electrodes. The researchers first placed ordinary sugar cubes on top of a polymer gel in a dish. After the dish was placed in a vacuum, heated in an oven, and washed, the sugar was dissolved away and the polymer gel took its place, resulting in stretchable polymer sponges. The pores of the polymer sponges were then filled with a conductive graphene-based solution to create "sponge electrodes," which the researchers achieved by immersing the sponges in the solution and squeezing them several times to soak it up.
As the researchers explained, the sponge's porous architecture provides a combination of stretchability, mechanical strength, fast sodium-ion transport, and large storage capacity. Tests showed that the full battery can be stretched to 50% beyond its original length, and that the strain is limited by the intrinsic properties of the polymer material. The researchers expect that modifying the polymer or developing a new nanoarchitectured elastomer could further increase the stretchability of the battery.
In its current form, the battery retains nearly 90% of its capacity after 100 cycles of stretching to 50% strain. This performance is sufficient to enable the researchers to mount the stretchable battery on an elbow brace, and demonstrate that the battery continues to power an LED when the user's arm is bent at different angles. The stretchable battery has potential applications in conformable health monitoring skin sensors, wearable communication devices, roll-up displays, and implantable medical devices.
In the future, the researchers plan to make further improvements to the battery, such as extending the lifetime and scaling up the design to larger-sized batteries. They anticipate that the sponge design can also be extended to other types of devices, such as energy-harvesting devices.
"Future directions will be focused on further improving the mechanical properties and electrochemical performance, along with lowering the manufacturing cost," Yu said.
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