Scientists build microbatteries with nanowire hearts

WASHINGTON - Robust, three-dimensional microbatteries that would charge faster and hold other advantages over conventional lithium-ion batteries are one-step closer to reality now.

Rice University researchers have built microbatteries, which could power new generations of remote sensors, display screens, smart cards, flexible electronics and biomedical devices.

The batteries employ vertical arrays of nickel-tin nanowires perfectly encased in PMMA, a widely used polymer best known as Plexiglas.

The scientists found a way to reliably coat single nanowires with a smooth layer of a PMMA-based gel electrolyte that insulates the wires from the counter electrode while allowing ions to pass through.

“In a battery, you have two electrodes separated by a thick barrier. The challenge is to bring everything into close proximity so this electrochemistry becomes much more efficient,” said Pulickel Ajayan.

“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 designs of batteries can be built from the nanoscale up,” said Sanketh Gowda, a graduate student in Ajayan’s lab.

“By increasing the height of the nanowires, we can increase the amount of energy stored while keeping the lithium ion diffusion distance constant.”

“The breakthrough here is the ability to put a conformal coat of PMMA on a nanowire over long distances. Even a small break in the coating would destroy it,” said postdoctoral researcher Arava Leela Mohana Reddy.

The process builds upon the lab’s previous research to build coaxial nanowire cables that was reported in Nano Letters last year. In the new work, the researchers grew 10-micron-long nanowires via electrodeposition in the pores of an anodized alumina template.

They then widened the pores with a simple chemical etching technique and drop-coated PMMA onto the array to give the nanowires an even casing from top to bottom. A chemical wash removed the template.

They have built one-centimeter square microbatteries that hold more energy and that charge faster than planar batteries of the same electrode length.hey feel the PMMA coating will increase the number of times a battery can be charged by stabilizing conditions between the nanowires and liquid electrolyte, which tend to break down over time.

The team is also studying how cycling affects nanowires that, like silicon electrodes, expand and contract as lithium ions come and go.

The work was reported this week in the online edition of the journal Nano Letters. (ANI)