TEKNIK ELEKTRONIKA

Researchers at Nanotek Instruments (USA), working in collaboration with scientists at Angstron Materials (USA) and Dalian University of Technology (China), have developed novel graphene electrodes for supercapacitors that could lead to capacitors with more than five times the energy density of currently available devices.

 

By using specially prepared crumpled sheets of graphene (carbon sheets only one atom thick), Nanotek increased the surface area of the electrodes so they could hold more charge. According to Nanotek's Bor Jang, lead author of a paper published in the online version of the journal Nano Letters, their aim is to bridge the energy density gap between capacitors and rechargeable batteries.

 

Tests with a coin-sized supercapacitor cell showed that the graphene electrodes could store 85.6 watt-hours of energy per kilogram. A practical device would therefore have an energy density of around 28 watt-hours per kilogram, since the electrodes typically account for one-third the weight of a capacitor. By comparison, current supercapacitors have energy densities of 5 to 10 watt-hours per kilogram, versus 40 to 100 watt-hours per kilogram for nickel metal hydride batteries and over 120 watt-hours per kilogram for lithium-ion batteries.

 

However, batteries are typically operated in the middle range of their full charge cycle, often using only about 20 to 50% of their total charge capacity. This means that supercapacitors with about 20% of the energy density of a rechargeable battery, but with short recharge time and almost unlimited lifetime, could be competitive in some applications. Furthermore, the chemical reactions that charge a battery take hours and degrade the electrodes after a few thousand cycles, while supercapacitors charge in minutes and can last millions of recharge cycles because they store charge electrostatically.

 

Image: Nano Letters

More info

Nanotek Instruments websiteNano Letters publication



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