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Vanadium oxide graphene could make more powerful batteries

Wed, 04/17/2013 - 18:36 -- Ruth Williams

A vanadium oxide (VO2) and graphene amalgamation could make more powerful lithium-ion batteries, according to a study at Rice University in Texas.

The research team has created a cathode material – a ribbon – that promises high energy and power density for batteries. The research will be presented in the American Chemical Society journal Nano Letters.

The ribbons are far thinner than a sheet of paper, ten nanometers thick, up to 600 nanometers wide and tens of micrometers in length. They potentially charge and discharge far quicker than current materials. Tests were carried out using cathodes built into half-cells that fully charged and discharged in 20 seconds and retained more than 90% of their capacity after more than 1,000 cycles.

"This is the direction battery research is going, not only for something with high energy density but also high power density," Pulickel Ajayan, materials scientist at Rice, said. "It's somewhere between a battery and a supercapacitor."

The ribbons are made from cheap and abundant materials using a hydrothermal process, which Ajayan thinks will be scalable to large quantities.

Vanadium oxide has long been considered as a potential cathode material, vanadium pentoxide is already in use in lithium-ion batteries due to its structure and high capacity. However, due to low electrical conductivity, oxides are slow to charge and discharge. Ajayan said this problem is overcome using the baked in high-conductivity graphene lattice, which serves as an outlet for electrons and a channel for ions.

"We think this is real progress in the development of cathode materials for high-power lithium-ion batteries," Ajayan said, his laboratory is developing paintable batteries, which the ribbons' ability to be dispersed in a solvent could make them a suitable component.

Shubin Yang, a graduate student scientist, said the challenges of production involved ensuring a constant condition for the co-synthesis of the VO2 with the graphene. This required the suspension of graphene oxide nanosheets with powdered vanadium pentoxide in water that is heated in an autoclave for hours. The vanadium pentoxide reduces to VO2, which crystallises into ribbons and the graphene oxide reduces to graphene, Yang said.