Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of Chemistry at Rice University said, “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.”  That is exactly a main point.  Congratulations are in order right off the start.

While Ajayan is working at the nano and micro level some of this will scale up.  Heads up –

The Rice team has moved a step closer to creating robust, three-dimensional microbatteries that would charge faster and hold other advantages over conventional lithium-ion batteries. They could power new generations of remote sensors, display screens, smart cards, flexible electronics and biomedical devices.

3-D Nanowire Battery Graphic. Click image for more info.

The batteries employ vertical arrays of nickel-tin nanowires perfectly encased in PMMA, a widely used polymer better known as Plexiglas. The Rice team found a way to reliably coat single nanowires with a smooth layer of a PMMA-based gel electrolyte that insulates the wires from the other counter electrode while allowing ions to pass through.

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.

The result is forests of coated nanowires — millions of them on a fingernail-sized chip — for scalable microdevices with much greater surface area than conventional thin-film batteries.  The theoretical capacity increase nears 150%.

3-D Nanowire Battery Nanowires

Second point – Ajayan explains, “You can’t simply scale the thickness of a thin-film battery, because the lithium-ion kinetics would become sluggish.”  Thus the design is going to act much faster.

Sanketh Gowda, a graduate student in Ajayan’s lab and postdoctoral researcher Arava Leela Mohana Reddy, worked for more than a year to refine the process.

“We wanted to figure out how the proposed 3-D designs of batteries can be built from the nanoscale up. By increasing the height of the nanowires, we can increase the amount of energy stored while keeping the lithium-ion diffusion distance constant,” said Gowda.

Reddy said, “To be fair, the 3-D concept has been around for a while. 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.” He said the same approach is being tested on nanowire systems with higher capacities.

Third point – The team believes 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.  They have built one-centimeter square microbatteries that hold more energy and that charge faster than planar batteries of the same electrode length. “By going to 3-D, we’re able to deliver more energy in the same footprint,” Gowda said.

In the latest Nano Letters paper the team explores their work in good detail. The most impressive part of the news is the intuitive use of the Plexiglas for the polymer coating and the conditioning it receives for use.  Actually the whole build is very impressive.

For scale up the process cost isn’t discussed.  But there are clues here of great significance for others in battery development.  The toughness of Plexiglas could offer a far more resilient battery beyond the performance gains.

This is a technology to watch.  Now that a 3-D build is shown to work, and quite well in the initial stage, the small lithium ion battery business has a viable source to begin further development.  How tall the rods can get, the variations on the PMMA mix, overall size, and seemingly endless questions and potential seem assured.

Further testing will also be quite interesting as another main issue for batteries is the operating temperatures.  Just how this design acts over temperature changes is of great interest.  If the rod coated with polymer can withstand wide temperature changes as well as the ions assaults over many cycles this technology might be supreme.

Moreover, the total raw lithium needed could also be reduced.  This list just goes on. For those interested in lithium ion technology the Nano Letters paper and particularly the supporting information are must reads.

Perhaps one worry exits, this team (including Rice graduate student Xiaobo Zhan; former Rice postdoctoral researcher Manikoth Shaijumon, now an assistant professor at the Indian Institute of Science Education and Research, Thiruvananthapuram, India; and former Rice research scientist Lijie Ci, now a senior research and development manager at Samsung Cheil Industries) will likely get intense attention from commercial developers.  Let’s hope they can stay working for a couple more years to work out the rest of the fundamentals.


6 Comments so far

  1. Pete on December 13, 2010 7:39 AM

    I believe that the most interesting part here is that dividing the battery into small separate reaction cells makes it last more cycles. Especially in large, expensive batteries for electric vehicles, having to pay half the price of the car every few years can be a deal breaker. Recycling should bring down the costs, but nothing beats improving battery life.

    I also recall a research group trying something similar with Li-S batteries a couple of years ago, but since then I have not heard anything new about that.

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