Researchers have discovered that graphene electrodes could lead to ultracapacitors with more than five times the energy density of today's commercial ultracapacitors. Practical devices based on the design could have an energy density of about 28 watt-hours per kilogram, almost one fourth of the energy density of a li-ion battery.
Researchers at Nanotek Instruments in Dayton, Ohio, have now made graphene electrodes that could lead to ultracapacitors with more than five times the energy density of commercial devices. By using graphene--atom-thick sheets of carbon--Nanotek increases the surface area of the electrodes in the ultracapacitors, boosting the amount of charge that they can store. "We are trying to bridge the performance gap between an ultracapacitor and a lithium-ion battery," says Nanotek's Bor Jang, the lead author of a paper published in the online version of the journal Nano Letters.
The company's tests of a coin-sized ultracapacitor cell show that the graphene electrodes could store 85.6 watt-hours of energy per kilogram. Since an electrode typically weighs about one-third of a full-size ultracapacitor, a practical device would have an energy density of around 28 watt-hours per kilogram, Jang says. By comparison, today's ultracapacitors have densities of 5 to 10 watt-hours per kilogram, while nickel metal hydride batteries and lithium-ion batteries boast 40 to 100 watt-hours per kilogram and over 120 watt-hours per kilogram respectively.