Technology firms and fashion businesses have long dreamed of developing wearable technology. Ever since smartphones enabled us to carry around with us portable computers the idea of incorporating electronic devices either into clothing or directly onto the skin has existed.

y using a forest of tiny carbon nanotubes as a raw material for flexible, electrically conductible supercapacitors, a nanotechnology team may now have found a way to make wearable devices a reality.

The problem with current wearable tech is that they require a bulky, heavy battery. They are often rigid and fragile, and so break easily. They are also prone to damage from moisture (either rain or sweat) and the person can easily overheat the device, or vice versa.

By using a crumpled mat of carbon nanotubes (CNTs) just two hundredths of a millimetre high, the researchers from Michigan State University believe they have developed supercapacitors strong enough to power circuitry, yet flexible enough and durable enough to be incorporated into clothing or skin.

As the MSU website states, “[This] discovery is the first to use crumpled standing CNTs for stretchable energy storage applications, which grow like trees with their canopies tangled on wafers. This forest, however, is merely 10-30 micrometers high. After transferred and crumpled, the CNT forest forms impressive stretchable patterns, like a blanket. The 3D interconnected CNT forest has a larger surface area and can be easily modified with nanoparticles or adapted to other designs.”

Prof. Changyong Cao, the lead-author of the study and the director at the Soft Machines and Electronics Laboratory at Michigan State University explained the advantages further, when he said, “It’s more robust; it’s truly a design breakthrough. Even when it’s stretched up to 300% along each direction, it still conducts efficiently. Other designs lose efficiency, can usually be stretched in only one direction or malfunction completely when they are stretched at much lower levels.”

The team have now published their results in the journal Advanced Energy Materials, which state that, “The crumpled CNT‐forest electrodes demonstrated good electrochemical performance and stability under either uniaxial (300%) or biaxial strains (300% × 300%) for thousands of stretching–relaxing cycles. The resulting supercapacitors can sustain a stretchability of 800% and possess a specific capacitance of 5 mF cm−2 at the scan rate of 50 mV s−1.”

Prof. Changyong Cao of Michigan State University

Additionally, the design can be enhanced as, “… the crumpled CNT‐forest electrodes can be easily decorated with impregnated metal oxide nanoparticles to improve the specific capacitance and energy density of the supercapacitors.”

Cao goes on to explain that, “The key to the success is the innovative approach of crumpling vertically aligned CNT arrays, or CNT forests. Instead of having a flat thin film strictly constrained during fabrication, our design enables the three-dimensionally interconnected CNT forest to maintain good electrical conductivity, making it much more efficient, reliable and robust.”

You can read more about the development of CNT films for wearable electronics by the University of Houston on this TeamTrade blog.  

While most people think of wearable technology in its basic form, such as an iWatch or FitBit device, the future of truly wearable electronics lies in devices so fine they can be woven into fabrics or sprayed onto T-shirts. Alternatively, the nanotube forests could be used towards the development of smart packaging.

On a medical level, nanotechnology specialists envisage smart skin patches for burn victims, electronic devices that can be incorporated into biological tissue or organs to track health, identify disease, or interact with doctors.

Given the levels of flexibility and the repeated stretch achieved with these CNT supercapacitors it is even possible that the devices could be self-powered. Nanoscale solar panels could power garments, while internal devices could be powered by the movement of the skin or organ involved.

Photo credit: T3, TeamTrade, MSU, & Nano