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March 30, 2013

Vanadium graphene ribbons for fast charging and discharging batteries

Hybrid ribbons of vanadium oxide (VO2) and graphene may accelerate the development of high-power lithium-ion batteries suitable for electric cars and other demanding applications. The ribbons created at Rice are thousands of times thinner than a sheet of paper, yet have potential that far outweighs current materials for their ability to charge and discharge very quickly. Cathodes built into half-cells for testing at Rice fully charged and discharged in 20 seconds and retained more than 90 percent of their initial 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,” Ajayan said. “It’s somewhere between a battery and a supercapacitor.”

In testing the new material, Yang and Gong found its capacity for lithium storage remained stable after 200 cycles even at high temperatures (167 degrees Fahrenheit) at which other cathodes commonly decay, even at low charge-discharge rates.

“We think this is real progress in the development of cathode materials for high-power lithium-ion batteries,” Ajayan said, suggesting the ribbons’ ability to be dispersed in a solvent might make them suitable as a component in the paintable batteries developed in his lab.


Hydrothermal processing of vanadium pentoxide and graphene oxide creates graphene-coated ribbons of crystalline vanadium oxide, which show great potential as ultrafast charging and discharging electrodes for lithium-ion batteries.
Image Credit: Ajayan Group at Rice University.





Although lithium ion batteries have gained commercial success owing to their high energy density, they lack suitable electrodes capable of rapid charging and discharging to enable a high power density critical for broad applications. Researchers have demonstrated a simple bottom-up approach toward single crystalline vanadium oxide (VO2) ribbons with graphene layers. The unique structure of VO2-graphene ribbons thus provides the right combination of electrode properties and could enable the design of high-power lithium ion batteries. As a consequence, a high reversible capacity and ultrafast charging and discharging capability is achieved with these ribbons as cathodes for lithium storage. A full charge or discharge is capable in 20 s. More remarkably, the resulting electrodes retain more than 90% of the initial capacity after cycling more than 1000 times at an ultrahigh rate of 190C, providing the best reported rate performance for cathodes in lithium ion batteries to date.


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