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New Self-Assembled Silicon-Carbon Nanocomposite Anodes for Li-ion Batteries Offer More Than 5X The Reversible Capacity of Graphite Anodes

15 March 2010

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This scanning electron micrograph shows carbon-coated silicon nanoparticles on the surface of the composite granules used to form the new anode. Source: Georgia Tech. Click to enlarge.

Researchers have developed a new high-performance anode structure for lithium-ion batteries based on silicon-carbon nanocomposite materials. Produced via large-scale hierarchical bottom-up assembly, the material contains rigid and robust silicon spheres with irregular channels for rapid access of Li ions into the particle bulk.

The large silicon volume changes on lithium ion insertion and extraction—which can cause structural problems leading to rapid capacity loss—are accommodated by the particle’s internal porosity. The researchers have shown reversible capacities more than five times higher than that of the state-of-the-art graphite anodes (1,950 mAh g-1) and stable performance. The synthesis process is simple, low-cost, safe and broadly applicable, they say, providing new avenues for the rational engineering of electrode materials with enhanced conductivity and power.

Details of the new self-assembly approach were published online in the journal Nature Materials on 14 March.

Development of a novel approach to producing hierarchical anode or cathode particles with controlled properties opens the door to many new directions for lithium-ion battery technology. This is a significant step toward commercial production of silicon-based anode materials for lithium-ion batteries.

—Gleb Yushin, an assistant professor in the School of Materials Science and Engineering at the Georgia Institute of Technology

Fabrication of the composite anode begins with formation of highly conductive branching structures made from carbon black nanoparticles annealed in a high-temperature tube furnace. Silicon nanospheres with diameters of less than 30 nanometers are then formed within the carbon structures using a chemical vapor deposition process. The silicon-carbon composite structures resemble “apples hanging on a tree.”

Using graphitic carbon as an electrically-conductive binder, the silicon-carbon composites are then self-assembled into rigid spheres that have open, interconnected internal pore channels. The spheres, formed in sizes ranging from 10 to 30 microns, are used to form battery anodes. The relatively large composite powder size—a thousand times larger than individual silicon nanoparticles—allows easy powder processing for anode fabrication.

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Proposed schematic for the formation of bulk Si-C nanocomposite electrodes via hierarchical bottom-up assembly. (a) annealed carbon black dendritic particles are (b), coated by Si nanoparticles; (c) composite particles are mixed with a sacrificial binder and compacted into an electrode with open interconnected internal channels. The electrode is then transformed into a solid bulk electrode during annealing. Such electrodes will not require polymeric binders and may exhibit enhanced stability, higher electrical conductivity and larger volumetric capacity. Source: Magasinki et al., Supplementary materials. Click to enlarge.

The internal channels in the silicon-carbon spheres serve two purposes. They admit liquid electrolyte to allow rapid entry of lithium ions for quick battery charging, and they provide space to accommodate expansion and contraction of the silicon without cracking the anode. The internal channels and nanometer-scale particles also provide short lithium diffusion paths into the anode, boosting battery power characteristics.

The size of the silicon particles is controlled by the duration of the chemical vapor deposition process and the pressure applied to the deposition system. The size of the carbon nanostructure branches and the size of the silicon spheres determine the pore size in the composite.

Production of the silicon-carbon composites could be scaled up as a continuous process amenable to ultra high-volume powder manufacturing, Yushin said. Because the final composite spheres are relatively large when they are fabricated into anodes, the self-assembly technique avoids the potential health risks of handling nanoscale powders, he added.

So far, the researchers have tested the new anode through more than a hundred charge-discharge cycles. Yushin believes the material would remain stable for thousands of cycles because no degradation mechanisms have become apparent.

In addition to Yushin, the paper’s authors included Alexandre Magasinki, Patrick Dixon and Benjamin Hertzberg—all from Georgia Tech—and Alexander Kvit from the Materials Science Center and Materials Science Department at the University of Wisconsin-Madison, and Jorge Ayala from Superior Graphite. The paper also acknowledges the contributions of Alexander Alexeev at Georgia Tech and Igor Luzinov from Clemson University.

The research was partially supported by a Small Business Innovation Research (SBIR) grant from the National Aeronautics and Space Administration (NASA) to Chicago-based Superior Graphite and Atlanta-based Streamline Nanotechnologies, Inc.

Resources

  • A. Magasinki, P. Dixon, B. Hertzberg, A. Kvit, J. Ayala, G. Yushin (2010) High-performance lithium-ion anodes using a hierarchical bottom-up approach. Nature Materials doi: 10.1038/nmat2725

March 15, 2010 in Batteries | Permalink | Comments (14) | TrackBack (0)

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Comments

This sounds very cool. We've gotten no indication that silicon nanowires could be produced at high volume and low cost, so this is the most encouraging Anode announcement yet, on the science.

Has anybody heard about an encouraging cathode announcement for Lithium, which could deliver the other half of the the capacity equation for rechargeable batteries?

Even if we're stuck with a cathode that can handle only ~450 mAh g-1, we can increase the size of the cathode 50%, reduce the anode 50%, and get a battery with maybe half again better power and volumetric density than today's lithium batteries.

This is good news but much more will come on the road to 1000+ Wh/Kg rechargeable batteries.

Many will be surprised on the progress that will be made between now and 2020.

This is just the tip of the Iceberg. We have entered a very interesting decade for improved e-storage units and electrified vehicles.

@HarveyD,

Why do you keep referring to 2020? Currently there are several hundred companies working on lithium batteries for possible BEV/PHEV. Many of the incremental improvements should show up in the next 2-4 years. The radical improvements of academia could show up in 3-5. 2020 is not a "happy" number...and I dare say it's also not the most likely.

In the progress of transportaion until 2020, it will be discovered that high energy and high power batteries are not needed because they are not even now needed for plug in hybrid vehicles.

Because the reactive elements of the sodium sulphur battery are pure elements, that reactive system seems to have an ability to have very high energy density. I am sure that some clever person in China, where there are fewer controls on research and engineering, can come up with a sodium-sulphur flow battery where the service station can just pump out the sodium sulfides and pump in more sodium and sulphur, if a truly electric long distance car is really needed.

The automated transportation system known as Skytran can be implemented at much lower costs than road ways and new electric automobiles with hundreds of pounds of batteries, and a slight modification to the idea which allows at least some of the Skytran vehicles to land and move a few miles on the ground will make such a system easy to initiate and expand. Magnetic suspension is not even a necesssary detail to work out.

Walking can be done without any new large high capacity batteries. ..HG..

@ Henry,

Um, I've got to say Henry that you're getting more "out there." Molten electrolyte refueling or taking a gondola everywhere? They are possible, but they seem to have substantial drawbacks that would inhibit replacing today's vehicle fleet.

There are so many breakthroughs coming on the battery front. EVs will have a decent market penetration by 2015 (over 1 million vehicles) and a very good one by 2020 (well over 15 million). Those are my predictions and I'll be glad to stick by them a just as much as the nay sayers and we'll see who is right.

We'll see $150/kWh and 1000Wh/kg batteries within 7-8 years and at that point it would be a miracle if gas was below $5 a gallon...more likely $6-7.

The findings (yes, findings...not some study with predictions) the finding of the Southern Company in Georgia over 15 years was that the average person started to get over range anxiety when they had a range of over 100 miles. It seems very small to us when we're used to 350 miles now, but when you realize you plug in every night at home and don't worry about it, people will laugh when they look back at the doom and gloom predictions.
A 150 mile range is plenty for the vast majority of us. We can stop having to find a gas station all the time and can simply plug in and charge up while at the grocery shopping or at the mall. The infrastructure will build out for that.

That guy need to do some jail time for such a hoax.

HB:

Using 200 Wh/Kg as the current high performance level + an 18% a year improvement rate gives 1050 Wh/Kg by 2020.

Batteries improvement rate of 18%/year was recently mentioned as being possible, by Panasonic, during the current decade.

If a 20%/year improvement rate is used, we could have 1000 Wh/Kg batteries (in mass production?) as early as 2018.

From last year:

http://www.rdmag.com/RD100-Awards-Pushing-The-Envelope-On-Li-Ion-Propulsion/

"Argonne and Envia Systems accomplish the task through a new lithium- and manganese-rich high-capacity material (NMC-HP). The material offers higher energy capacity than existing systems because of its high stability at a voltage of 4.3 V. At this high voltage, the material offers 180 mAh/g and a 3.7 average potential. With a price point of $190 per kWh, the material is also more cost-effective than any current competitors.."

..but try and find it at Walmart..

Today Envia and Argonne are shooting for 400 W/kg. Argonne's layered manganese composite cathodes seem to be the best at 250 mAh/g and are already licensed to BASF and other companies for commercialization. Combining them with Si-C composite anode materials from GA Tech, Argonne, and others, 20%/year may be too conservative. I'll bet the Si-C nanocomposites are cheaper to make than Si nanowires.

"market penetration by 2015 (over 1 million vehicles)"

Is that worldwide or U.S.? If it is U.S. I will take that bet.

I was thinking world wide. But let's make it fun and say US (Of course, that's cumulative, not 1 million in year 2015....I'm not that crazy). :-)

I still think we're over estimating range anxiety. Battery improvements like this will make a huge difference sooner than we expect.

I'm going to see if Don Francis, who ran the Southern Company's EV program for 15 years, has the old data he was telling me about.

He said they found in the real world that people absolutely got comfortable with anything above 100 miles range and that range anxiety went away after they had a chance to see how it felt in every day conditions.

This was not a survey of "potential owners" but of the people actually living with them every day for years.

Below is another link to similar data from a recent survey:
http://www.msnbc.msn.com/id/35352973/ns/business-autos/

Let's say Prius sells at 200,000 units per year and we are saying that cumulative sales of EVs like the Leaf will total 1 million units by 2015, that is a long shot.

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