Researchers from Stanford University, United States, have found that wrapping sulfur nanoparticles in graphene sheets can result in a promising cathode material for rechargeable lithium-sulfur batteries that could be used for powering electric vehicles on a large scale. Combined with silicon-based anodes, these new cathodes could lead to rechargeable batteries with a significantly higher energy density than is currently possible. Current rechargeable lithium batteries used in electric vehicles have a weak spot – the cathode materials – which have specific capacities much lower than that of the anode materials. In order for electric vehicles to be competitive with gasoline-powered vehicles, the energy and power densities of such batteries need to be improved. The researchers turned to sulfur as a way to improve the cathodes, which has a theoretical specific capacity five times higher than those of traditional cathode materials, and is also low in cost and has a benign environmental impact. Sulfur is, however, a poor conductor. The researchers found that adding carbon to sulfur, and adjusting the sulfur by coating it with polyethylene glycol, its electrical conductivity can be improved. According to Yi Cui, one of the researchers, “We developed a strategy of graphene wrapping to overcome many issues related to using sulfur as lithium-ion battery cathodes. We have shown excellent cycling performance,” he said, adding, “Overall, the biggest challenges facing rechargeable batteries for electric vehicles are increasing the energy density and reducing the cost. Using high-energy and low-cost materials such as sulfur is very attractive.”
http://www.physorg.com/news/2011-07-rechargeable-lithium-sulfur-batteries-boost-graphene.html