Fabric-like supercapacitor customisable for wearable electronics

Scientists at Nanyang Technological University, Singapore have created a customisable, fabric-like power source that can be cut, folded or stretched without losing its function, making it suitable for wearable electronics. Writing in the journal Advanced Materials, the team explained that their wearable power source, a supercapacitor, works like a fast-charging battery and can be recharged many times.

Crucially, they have made their supercapacitor customisable or ‘editable’, meaning its structure and shape can be changed after it is manufactured — while retaining its function as a power source. Existing stretchable supercapacitors are made into predetermined designs and structures, but the new invention can be stretched multidirectionally and is less likely to be mismatched when it is joined up to other electrical components.

“Although some progress has been made on stretchable supercapacitors, traditional stretchable supercapacitors fabricated by predesigning structured electrodes for device assembling still lack the device-level editability and programmability,” the researchers wrote. “To adapt to wearable electronics with arbitrary configurations, it is highly desirable to develop editable supercapacitors that can be directly transferred into desirable shapes and stretchability.”

The team’s supercapacitor is made of strengthened manganese dioxide nanowire composite material. While manganese dioxide is a common material for supercapacitors, the ultralong nanowire structure, strengthened with a network of carbon nanotubes and nanocellulose fibres, allows the electrodes to withstand the associated strains during the customisation process.

When edited into a honeycomb-like structure, the supercapacitor has the ability to store an electrical charge four times higher than most existing stretchable supercapacitors. In addition, when stretched to four times its original length, it maintains nearly 98% of the initial ability to store electrical energy, even after 10,000 stretch-and-release cycles.

The team’s experiments also show that when the editable supercapacitor was paired with a sensor and placed on the human elbow, it performed better than existing stretchable supercapacitors. It was able to provide a stable stream of signals even when the arm was swinging, which were then transmitted wirelessly to external devices — similarly to devices that captures a patient’s heart rate.

The researchers believe that the editable supercapacitor could be easily mass-produced as it would rely on existing manufacturing technologies. Production cost will thus be low, estimated at about AU$0.12 to produce 1 cm² of the material. The team has filed a patent for the technology.

“A reliable and editable supercapacitor is important for development of the wearable electronics industry,” said Professor Chen Xiaodong, leader of the research. “It also opens up all sorts of possibilities in the realm of the Internet of Things when wearable electronics can reliably power themselves and connect and communicate with appliances in the home and other environments.

“My own dream is to one day combine our flexible supercapacitors with wearable sensors for health and sports performance diagnostics. With the ability for wearable electronics to power themselves, you could imagine the day when we create a device that could be used to monitor a marathon runner during a race with great sensitivity, detecting signals from both under- and over-exertion.”

“Customisable and versatile, these interconnected, fabric-like power sources are able to offer a plug-and-play functionality while maintaining good performance,” added Dr Loh Xian Jun, a co-author on the research. “Being highly stretchable, these flexible power sources are promising next-generation ‘fabric’ energy storage devices that could be integrated into wearable electronics.”

Image caption: The supercapacitor functions well even when stretched. Image credit: NTU Singapore.