Published on February 17th, 2014 | by Tina Casey


Don’t Look Now, But Your Next EV Battery Could Look Like A Pomegranate

February 17th, 2014 by  

Lithium-ion batteries have been the gold standard for powering electric vehicles, but with fuel cells breathing down their necks, the pressure is on to come up with next-generation performance improvements. A team of researchers has come up with a solution based on the structure of a pomegranate, which could combine greater efficiency with commercial-scale durability.

The solution addresses one weak link, the anode (the anode is the negative electrode, which stores energy as you charge up the battery), so let’s dig in and see what this new pomegranate battery is all about.

pomegranate solves Li-ion battery problem

“Pomegranate” battery by Greg Stewart/SLAC.

A Carbon Solution For Your Silicon Problems

Conventional Li-ion batteries use an anode based on graphite, which is all well and good in terms of durability but not in terms of efficiency. For that, researchers have been making eyes at silicon, which has the potential to store ten times more charge than graphite.

However, the problem is that silicon is brittle. As the battery charges silicon swells, and as the battery discharges it shrinks. All that activity causes the silicon to flake apart, and react with the electrolyte to form a “gunk” that sticks to the anode, interfering with its efficiency.

A couple of promising avenues of research have emerged toward solving the problem, one being reinforcement by a carbon nanotube “scaffolding,” devised by a team at the University of North Carolina.

A similar approach taken by researchers at Lawrence Berkeley National Laboratory involves sandwiching nano-layers of silicon with another form of carbon, namely our favorite nanomaterial of the new millennium, graphene.

The Pomegranate Battery Solution

The “pomegranate” solution is also based on carbon but it takes a different tack.

It was developed by a team based at the Stanford Institute for Materials and Energy Sciences, a partnership with the Department of Energy’s SLAC National Accelerator Laboratory.

In this project, the researchers previously devised a method for encasing nanoparticles  of silicon in carbon “shells.” The particles are so small that they cannot be broken down into smaller pieces when they swell and shrink, and the carbon shell provides enough room to accommodate the change in size.

The current stage of development draws on microemulsion, a process common across a number of conventional industries including cosmetics and paint manufacturing. The idea is to make clusters of the shell-encased silicon nanoparticles and then coat them with a second layer of carbon.

As with a pomegranate, what you get is a single relatively large sphere that has just a fraction of the total surface area of all the shell-encased nanoparticles within it. That smaller surface area means that there is less exposure to the electrolyte, which reduces the “gunk” factor.

LI-ion battery based on pomegranate

Shell-encased silicon nanoparticles by Nian Liu, Zhenda Lu and Yi Cui/Stanford.

Don’t Hold Your Breath For That Pomegranate Battery — Wait, What?

When we cover research projects like this we usually include a don’t-hold-your-breath reminder, since there is usually a long (very long) trail from the lab to commercial development.

However, the “pomegranate battery” research has already been under way for at least eight years in the lab of Stanford researcher Yi Cui, who also happens to be the founder of a Li-ion battery company called Amprius.

If Amprius rings a bell, last month the company raised $30 million in funding to commercialize the first-generation version of its silicon based Li-ion batteries, with more goodies in store in the future when the company introduces its next-generation version.

For the record, the company also made news last month when former Energy Secretary Steven Chu joined its Board of Directors last month.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

  • driveby

    “Lithium-ion batteries have been the gold standard for powering electric vehicles, but with fuel cells breathing down their necks, the pressure is on to come up with next-generation performance improvements. ..”

    Is that similar to how electric vehicles breath down the necks of ICE vehicles?

    ..back on topic:
    As for the carbon coated small carbon balls, which contain the silicon lithium stuff.. in what are the ‘big’ pomegranate balls embedded later?

    And wasn’t there some sulfur in those small balls before?

  • jburt56

    Showing you should never take the pome for granted.

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