Researchers at MIT have developed a new type of flexible, nanowire-based supercapacitor with performance vastly exceeding its graphene counterpart. It could find use as the ideal energy source for the next generation of fitness trackers and other wearable devices.

Battery performance is one of the main bottlenecks for the increasingly popular smartwatches and fitness trackers. The issue is that the very strict size constraints for these devices make it so that their very small energy cells struggle to deliver the quick bursts of power needed to broadcast data wirelessly, especially over long distances.

A better way forward could be to use small supercapacitors, which can deliver quick bursts of high power, to complement batteries. Researchers are rushing to develop high-performance supercapacitors from a number of materials. Carbon nanotubes and graphene, however, remain two of the strongest candidates because their large surface area can pack a large number of ions, which means more energy can be stored inside a small and light device.

The new approach proposed by MIT uses yarns made from niobium nanowires as the electrodes in tiny supercapacitors. According to the researchers, this new nanowire-based supercapacitor features a high volumetric power density (power per unit volume) of 55 W/cc and energy density (energy per unit volume) of 7 mWh/cc, which are, respectively, two and five times higher than that of carbon nanotube-based yarns. In addition, the device also occupies a very small volume and is likely to be able to be produced at low cost.

As with its carbon-based counterparts, the niobium-based nanowires achieve high performance through high conductivity and high surface area, but in contrast with them, the MIT supercapacitors can do without a metal backing, which saves substantial amounts of space. This is especially important if these devices are to find use in wearable devices, where space is very much at a premium. Niobium is also a fairly abundant material, so the supercapacitors are expected to be relatively cheap and easy to produce.

Besides fitness and health tracking, the niobium yarn supercapacitors may also find use wherever small bursts of power are needed, such as for powering tiny robots or in extreme temperature environments (since niobium has a very high melting point of 2,500 °C/4,500 °F). Because the material is highly flexible and only 140 nanometers in diameter, it could also be woven into fabrics to create wearable devices with an even lower footprint.

The material has only been produced at the laboratory scale so far, but the researchers say they're now trying to design and implement a version of the supercapacitor that can be easily mass-produced.

The supercapacitor in described in a paper that recently appeared in the journal ACS Applied Materials and Interfaces.

Source: MIT

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