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Graphene helps Li-Ion batteries charge faster

18 August 2010 News

Battery performance and form factors have been major constraints in the development of handheld computing and communication devices.

There is intense demand for ever-greater charge densities and cycle stabilities from the consumer electronics industry and lithium-ion technology, the leading technology option for such devices, has struggled to keep up. A major challenge has been the trade-off in battery design between higher capacity and recharge speed, which has imposed fundamental limitations on the performance of such batteries.

Now, novel battery materials developed at the Pacific Northwest National Laboratory (PNNL) of the Department of Energy and Vorbeck Materials, could enable lithium-ion batteries used in a wide range of applications from electric vehicles to cellphones to recharge in minutes rather than hours.

Researchers at PNNL, in collaboration with researcher Ilhan Aksay at Princeton University and Vorbeck Materials, have demonstrated that small quantities of graphene can improve the power and cycling stability of lithium-ion batteries dramatically without significant impact on their energy storage capacity. This discovery could enable designers to work around the traditional trade-off between capacity and power. The researchers believe that the new battery materials with graphene could cut recharge time to less than 10 minutes from the current norm of two to five hours for full recharge of cellphone batteries.

Vorbeck Materials licensed its method for making crumpled or defective graphene in large quantities from Aksay, a professor of chemical engineering at Princeton University in 2006, and have targeted a number of applications. They make conductive inks based on graphene to print extremely low-cost radio frequency identification (RFID) antennas and electrical contacts for flexible displays, and have an agreement with BASF, the German chemicals specialist.

The graphene-based ink is significantly cheaper than competing silver-based inks, although it has less conductivity. Moreover, the graphene-based inks, unlike the silver-based alternative, do not require heat treatment and therefore can be printed on to polymer substrates.

The newly patented method to manufacture defective graphene involves oxidisation of graphite with acids and their separation into atom-thin sheets. The sheets of expanded graphite are forced apart by rapid heating, causing carbon dioxide build-up. The sheets are then heated to remove the oxygen groups. According to Aksay, the conductivity is close to that of pure graphene, but the sheets are crumpled so they do not stack together again. His research group developed monitoring methods to improve the yield and ensure complete separation of graphene sheets, enabling rapid commercialisation. Vorbeck markets this unique graphene material under the brand name Vor-x.

For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)18 464 2402, patrick.cairns@frost.com, www.frost.com





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