This is more battery research and in thiscase they are growing a forest of nano batteries in order to gain in energy density. No one really knows what the successfulprotocol will ultimately be, so we must push forward on every good idea.
This looks a long ways from been optimized soit is good to see early success in methodology. This is something that could be commercialized into circuit boards and miniaturedevices.
Anyway, the battery rush continues.
Better batteries from the bottom up
CONTACT: Mike Williams
The batteries employ vertical arrays of nickel-tinnanowires perfectly encased in PMMA, a widely used polymer best known asPlexiglas. The Rice laboratory of Pulickel Ajayan found a way to reliably coatsingle nanowires with a smooth layer of a PMMA-based gel electrolyte thatinsulates the wires from the counter electrode while allowing ions to passthrough.
The work was reported this week in the online edition ofthe journal Nano Letters.
"In a battery, you have two electrodes separated by athick barrier," said Ajayan, professor in mechanical engineering andmaterials science and of chemistry. "The challenge is to bring everythinginto close proximity so this electrochemistry becomes much moreefficient."
Ajayan and his team feel they've done that by growingforests of coated nanowires -- millions of them on a fingernail-sized chip --for scalable microdevices with greater surface area than conventional thin-filmbatteries. "You can't simply scale the thickness of a thin-film battery,because the lithium ion kinetics would become sluggish," Ajayan said.
"We wanted to figure out how the proposed 3-D designsof batteries can be built from the nanoscale up," said Sanketh Gowda, agraduate student in Ajayan's lab. "By increasing the height of thenanowires, we can increase the amount of energy stored while keeping thelithium ion diffusion distance constant."
The researchers, led by Gowda and postdoctoral researcherArava Leela Mohana Reddy, worked for more than a year to refine the process.
"To be fair, the 3-D concept has been around for awhile," Reddy said. "The breakthrough here is the ability to put aconformal coat of PMMA on a nanowire over long distances. Even a small break inthe coating would destroy it." He said the same approach is being testedon nanowire systems with higher capacities.
The process builds upon the lab's previous research tobuild coaxial nanowire cables that was reported in Nano Letters last year. Inthe new work, the researchers grew 10-micron-long nanowires viaelectrodeposition in the pores of an anodized alumina template. They thenwidened the pores with a simple chemical etching technique and drop-coated PMMAonto the array to give the nanowires an even casing from top to bottom. Achemical wash removed the template.
They have built one-centimeter square microbatteries thathold more energy and that charge faster than planar batteries of the sameelectrode length. "By going to 3-D, we're able to deliver more energy inthe same footprint," Gowda said.
They feel the PMMA coating will increase the number oftimes a battery can be charged by stabilizing conditions between the nanowiresand liquid electrolyte, which tend to break down over time.
The team is also studying how cycling affects nanowiresthat, like silicon electrodes, expand and contract as lithium ions come and go.Electron microscope images of nanowires taken after many charge/dischargecycles showed no breaks in the PMMA casing -- not even pinholes. This led theresearchers to believe the coating withstands the volume expansion in theelectrode, which could increase the batteries' lifespans.
Co-authors are Rice graduate student Xiaobo Zhan; formerRice postdoctoral researcher Manikoth Shaijumon, now an assistant professor atthe Indian Institute of Science Education and Research, Thiruvananthapuram,India; and former Rice research scientist Lijie Ci, now a senior research anddevelopment manager at Samsung Cheil Industries.
The Hartley Family Foundation and
funded the research. Rice University