The Rice University lab of materials scientist Pulickel Ajayan determined that the well-studied material is a superior cathode for batteries that could supply both high energy density and significant power density.
- Hybrid ribbons of vanadium oxide (VO2) and graphene may accelerate the development of high-power lithium-ion batteries.
The research appears online this month in the American Chemical Society journal Nano Letters.
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.
The ribbons also have the advantage of using relatively abundant and cheap materials.
Vanadium oxide has long been considered a material with great potential, and in fact vanadium pentoxide has been used in lithium-ion batteries for its special structure and high capacity. But oxides are slow to charge and discharge, due to their low electrical conductivity. The high-conductivity graphene lattice that is literally baked in solves that problem nicely, he said, by serving as a speedy conduit for electrons and channels for ions.
The atom-thin graphene sheets bound to the crystals take up very little bulk. In the best samples made at Rice, fully 84 percent of the cathode’s weight was the lithium-slurping VO2, which held 204 milliamp hours of energy per gram. The researchers, led by Rice graduate student Yongji Gong and lead author Shubin Yang, said they believe that to be among the best overall performance ever seen for lithium-ion battery electrodes.
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.
Co-authors of the new paper are Rice graduate students Daniel Hashim and Lulu Ma; research scientist Zheng Liu; former Rice visiting researcher Liang Zhan, now an associate professor at East China University of Science and Technology in Shanghai; and faculty fellow Robert Vajtai. Ajayan is the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of mechanical engineering and materials science, chemistry, and chemical and biomolecular engineering.
The work was funded by the U.S. Army Research Office and the Office of Naval Research through a Multidisciplinary University Research Initiative grant and a National Science Foundation Graduate Research Fellowship grant.