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New process for synthesizing nano-tin/carbon composite spheres for high-performance Li-ion anode material

10 January 2013

Xu
Cycling performance at 0.02−3 V and 200 mA/g of the nano-Sn/C composite. Credit: ACS, Xu et al. Click to enlarge.

Researchers at the University of Maryland have developed a new process—aerosol spray pyrolysis—to synthesize nano-Sn/C (nano-tin/carbon) composites for a Li-ion anode with uniformly dispersed 10 nm nano-Sn particles within a spherical carbon matrix. The discharge capacity of nano-Sn/C composite sphere anodes maintains the initial capacity of 710 mAh/g after 130 cycles at 0.25 C. The nano-Sn/C composite sphere anodes can provide ∼600 mAh/g even at a high rate of 20 C.

In a paper in the ACS journal Nano Letters, the team attributes the “exceptional” performance to the unique nano-Sn/C structure, adding that to the best of their knowledge, such high-rate performance for tin anodes has not been reported previously. Broadly, the benefits of the structure are:

  1. the carbon matrix offers mechanical support to accommodate the stress associated with the large volume change of nano-Sn when undergoing lithium insertion and extraction, thus alleviating pulverization;

  2. the carbon matrix prevents Sn nanoparticle agglomeration upon prolonged cycling; and

  3. carbon network provides continuous path for Li ions and electrons inside the nano-Sn/C composite spheres.

Tin anodes have attracted much attention because it delivers a capacity up to three times higher than that of graphite. Theoretically, one tin atom can maximally react with 4.4 lithium atoms to form Li4.4Sn alloy, reaching a capacity of 993 mAh/g. However, the large amount of lithium insertion/extraction into/from Sn causes a large volume change (about 300%), which causes pulverization of tin particles and loss of contact with current collector, resulting in poor electrochemical performance.

Extensive efforts have been made to improve the electro- chemical behavior of Sn anodes. The most effective approaches include (1) reducing Sn particle size to nanoscale (<10 nm) to efficiently mitigate the absolute strain induced by the large volume change during lithiation/delithiation, and retard particle pulverization; (2) using nano-Sn with uniform particle size (narrow size distribution) to generate uniform stress/strain over the entire electrode during lithiation/delithiation, preventing local cracking; (3) uniformly dispersing nano-Sn in a conductive matrix (such as carbon) to accommodate volume change and maintain the mechanical integrity of the composite electrode. Clearly, a Sn/C composite with uniform tin nanoparticles (<10 nm) dispersed in a carbon matrix would be an ideal anode for Li-ion batteries.

...In this paper, we introduce aerosol spray pyrolysis to realize the ideal structure with nanograin Sn uniformly dispersed in a spherical conductive carbon matrix.

—Xu et al.

Xu2
(a) Schematic diagram, (b) TEM image, and (c,d) high- resolution images of the nano-Sn/C composite particles. Insert: SAED image. Credit: ACS, Xu et al. Click to enlarge.

The new process overcomes the difficulties—due to the low melting point of tin and the tendency of grain grow—in creating well-dispersed ultra-small tin nanoparticles within a carbon matrix.

The key to the process is the rapid heating of precursor droplets, allowing the quick formation of tin nanograins and the carbon frame. The short residence time and rapid subsequent cooling enables the freezing of the structure to nonaggregated and uniformly sized nano-Sn grains in a carbon matrix.

The electrochemical performance is superior to the nano-Sn/C composite anodes synthesized using other techniques. Meanwhile, the synthesis of aerosol spray pyrolysis is a widely used technique for commercial nanomaterials and easily scaled up, making nano- Sn/C composite very promising and attractive as an anode material for lithium-ion batteries.

—Xu et al.

Resources

  • Yunhua Xu, Qing Liu, Yujie Zhu, Yihang Liu, Alex Langrock, Michael R. Zachariah, and Chunsheng Wang (2013) Uniform Nano-Sn/C Composite Anodes for Lithium Ion Batteries Nano Letters doi: 10.1021/nl303823k

January 10, 2013 in Batteries | Permalink | Comments (12) | TrackBack (0)

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Comments

If this process can be mass produced at an affordable cost, if could become the foundation for a new family of higher performance batteries by or before 2020?

HarveyD

you said it so many times before... do you think it will speed up the process repeating the same wish all the time ?

Each advance helps. It is my guess that better batteries will come to market about the same time that people start to accept EVs.

This looks great, but one question:

Why the hell does every new advance coming out seem to stop between 50-100 cycles in testing? If they were testing at 25C rates, it couldn't take more than a couple of days to test 1,000 cycles or even 2,000 cycles.

So does it "fall off a cliff" performance wise at 150 cycles and they just don't want to tell us that? Seriously, I always wonder about that.

Tree...mass production of higher performance lower cost batteries by 2020 is going to happen. The technologies exist at the 'lab' level and 8 years should be enough to fine tune and start mass production of at least half a dozen of them.

There will be a few setbacks alone the way. A few battery packs will blow up or catch fire as did the first steam engines. Opponents will try their best to use those incidents for their pro Oil-NG-SG cause.

The next decade will confirm the superiority of EVs and convince many that 2, 3, 4, 6+ wheels electrified vehicles (HEVs, PHEVs, BEVs) of all size are gaining ground against ICEVs.

Money ($2T to $3+T) will move from OIL & NG/SG to clean electricity production and distribution as it did from horses and buggies to ICEVs 120+ years ago.

HarveyD

in my experience, when you see so many different solutions competing on a problem it means that you are still far from a real product and that the problem is really tough. When everybody focus on the same solution yes it is getting close. So far I see every lab trying a bit of everything , so prediction a precise timeline like you do is based on what exactly ?

Faith...we went to the moon and did the Manhattan Project. Past performance is not an absolute predictor of future outcomes. You can not schedule a unique masterpiece that has never been done before.

Dave D
When you see a flat capacity loss after 100+ cycles it's reasonable to expect that to continue.

JRP3,

I would assume that as well. Hell, I'd love to assume that. But if it's true then why don't they just carry out the testing for a few thousand cycles and blow us away.

Davemart would be so excited he couldn't see straight! LOL

You know I'm just joking right DaveMart :-)

By the way, how bad is the weather? I'm flying to London Sunday.

Tree....

ICEs technologies have developed half a dozen different ways. One to 16 cyls gasoline and diesel, jets, ramjets, rotary ICE, hydrogen rockets etc. Tires, transmissions etc also when through many simultaneous technologies.

Future FC and Battery technologies will probably also develop half a dozen different ways.

No one technology may remain the leader for a very long time.

That's evolution....

Professors and researchers seek funding. In battery materials, it's easy to show promising results in half cells or against lithium metal. These tend to allow the basic electrochemical performance to be evaluated, but in full cells with higher voltage differences between the cathode and anode, many of the degradation mechanisms kick-in. These guys should cycle against NMC or something like that and then we can talk about the potential. All we know thus far is theoretical capacity. Without full cell testing, cycling numbers are irrelevant. Nice synthesis though. They should apply it to sulfur nanoparticle encapsulation for cathodes. Might be a trickier chemistry though.

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