Development of a "Stretchable Power Source" That Maintains Performance on the Body [Reading Science]

Maintains 95% storage capacity even when stretched fourfold...Paving the way for commercialization of skin-attachable sensors

Wearable devices that adhere to the skin are becoming part of everyday life, but their power sources have still remained in the form of "rigid batteries." Because these power units cannot follow the movements of the human body, they have undermined comfort and limited the range of applications. A Korean research team has now presented a "stretchable power source" that could fundamentally change these limitations.

The National Research Foundation of Korea (NRF) announced that a research team led by Professor Yun Jinhwan at the University of Seoul has developed a highly stretchable supercapacitor whose storage capacity hardly decreases even when stretched up to four times its original length. This achievement is being evaluated as a core power technology that will accelerate the commercialization of skin-attachable sensors and next-generation wearable devices.

A supercapacitor attached to the arm keeps an LED steadily lit even when the elbow is bent at angles from 0 to 90 degrees. This demonstrates that power supply is maintained during body movement. Provided by Professor Yoon Jinhwan, University of Seoul

A supercapacitor is an energy storage device that stores electric charge on the surface of its electrodes, unlike batteries. Because it does not rely on chemical reactions like batteries do, it can be charged and discharged at high speed within a few seconds and shows little performance degradation even after repeated use, allowing it to instantly store small amounts of energy generated by body movement. However, conventional supercapacitors have had a major limitation in that their storage capacity drops significantly when they are stretched or deformed.

The research team solved this problem with two key technologies. First, they mixed manganese oxide, carbon nanotubes, and a conductive polymer into soft silicone rubber to create a flexible electrode, and then treated it with phosphoric acid to transform it into a needle-shaped manganese phosphate nanowire structure about one ten-thousandth the thickness of a human hair. This structure maintains pathways for electric current even when the electrode is stretched, thereby securing both stretchability and conductivity.

On top of this, they applied an amphoteric ion-gel electrolyte with strong adhesive properties. By forming chemical bonds between the electrode and the gel through ultraviolet treatment, they ensured that the electrode and electrolyte do not separate even after more than 10,000 cycles of stretching and releasing.

The supercapacitor developed in this way maintained more than 95% of its storage capacity even when stretched by 300%. When attached to the arm, an LED remained stably lit while the elbow was bent from 0 to 90 degrees, and tests also confirmed that it can be used for wireless charging of a smartphone. The team explains that this represents world-class performance that far surpasses existing technologies.

Professor Yun Jinhwan said, "This technology can be used as a core power component for next-generation wearable devices," adding, "It is expected to expand into fields that require high stretchability and stability, including electronic skin that is directly attached to the body to measure biosignals, as well as virtual-reality haptic suits and wearable devices for rehabilitation therapy."

This research was carried out with support from the Leading Research Center Program and the Korea-Czech Joint Research Program funded by the Ministry of Science and ICT and the National Research Foundation of Korea, and it was published online on January 7 in Energy Storage Materials, an international journal in the field of energy materials.

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