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New conductive polymer addresses volumetric change issue with silicon anodes for Li-ion batteries; high-capacity and longer cycle life reported

23 September 2011

Lbl1
At left, a traditional approach combines Si (blue spheres) with a polymer binder (light brown) plus carbon (dark brown spheres). Repeated swelling and shrinking eventually breaks contacts among the conducting carbon particles. At right, the new conductive polymer (purple) continues to bind tightly to the Si particles despite repeated swelling and shrinking. Click to enlarge.

A team of scientists at the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has developed new polyfluorene-based conductive polymers that address the long-standing issue of volumetric change in high-capacity silicon (Si) anodes for Li-ion batteries. A combination of synthesis, spectroscopy and simulation techniques tailors the electronic structure of the polymer to enable in situ lithium doping.

The tailored conductive polymer continues to bind closely to the lithium-storing silicon particles even as they expand to more than three times their volume during charging and then shrink again during discharge. Composite anodes based on this polymer and commercial Si particles exhibit 2,100 mAh g−1 in Si after 650 cycles without any conductive additive. A paper on their work is published in the journal Advanced Materials.

High-capacity lithium-ion anode materials have always confronted the challenge of volume change—swelling—when electrodes absorb lithium. Most of today’s lithium-ion batteries have anodes made of graphite, which is electrically conducting and expands only modestly when housing the ions between its graphene layers. Silicon can store 10 times more—it has by far the highest capacity among lithium-ion storage materials—but it swells to more than three times its volume when fully charged.

—Gao Liu of Berkeley Lab’s Environmental Energy Technologies Division (EETD)

Many approaches have been proposed to solving the volumetric change issue, which causes rapid capacity fading; some are prohibitively costly. One less-expensive approach has been to mix silicon particles in a flexible polymer binder, with carbon black added to the mix to conduct electricity. Unfortunately, the repeated swelling and shrinking of the silicon particles as they acquire and release lithium ions eventually push away the added carbon particles. What’s needed is a flexible binder that can conduct electricity by itself, without the added carbon.

Conducting polymers aren’t a new idea, but previous efforts haven’t worked well, because they haven’t taken into account the severe reducing environment on the anode side of a lithium-ion battery, which renders most conducting polymers insulators.

—Gao Liu

One such experimental polymer, called PAN (polyaniline), has positive charges; it starts out as a conductor but quickly loses conductivity. An ideal conducting polymer should readily acquire electrons, rendering it conducting in the anode’s reducing environment.

The signature of a promising polymer would be one with a low value of the state called the lowest unoccupied molecular orbital, where electrons can easily reside and move freely. Ideally, electrons would be acquired from the lithium atoms during the initial charging process. Liu and his postdoctoral fellow Shidi Xun in EETD designed a series of such polyfluorene-based conducting polymers (PFs).

When Liu discussed the excellent performance of the PFs with Wanli Yang of Berkeley Lab’s Advanced Light Source (ALS), a scientific collaboration emerged to understand the new materials. Yang suggested conducting soft x-ray absorption spectroscopy on Liu and Xun’s candidate polymers using ALS beamline 8.0.1 to determine their key electronic properties. Soft x-ray spectroscopy can tell the researchers where the ions and electrons are and where they move, notes Yang.

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Transmission electron microscopy reveals the new conducting polymer’s improved binding properties. At left, silicon particles embedded in the binder are shown before cycling through charges and discharges (closer view at bottom). At right, after 32 charge-discharge cycles, the polymer is still tightly bound to the silicon particles, showing why the energy capacity of the new anodes remains much higher than graphite anodes after more than 650 charge-discharge cycles during testing. Click to enlarge.

Compared with the electronic structure of PAN, the absorption spectra Yang obtained for the PFs stood out immediately. The differences were greatest in PFs incorporating a carbon-oxygen functional group (carbonyl).

Lin-Wang Wang of Berkeley Lab’s Materials Sciences Division (MSD) and his postdoctoral fellow, Nenad Vukmirovic, conducted ab initio calculations of the polymers at the Lab’s National Energy Research Scientific Computing Center (NERSC).

The simulation revealed that the lithium ions interact with the polymer first, and afterward bind to the silicon particles. When a lithium atom binds to the polymer through the carbonyl group, it gives its electron to the polymer—a doping process that significantly improves the polymer’s electrical conductivity, facilitating electron and ion transport to the silicon particles.

Having gone through one cycle of material synthesis at EETD, experimental analysis at the ALS, and theoretical simulation at MSD, the positive results triggered a new cycle of improvements. Almost as important as its electrical properties are the polymer’s physical properties, to which Liu now added another functional group, producing a polymer that can adhere tightly to the silicon particles as they acquire or lose lithium ions and undergo repeated changes in volume.

Scanning electron microscopy and transmission electron microscopy at the National Center for Electron Microscopy (NCEM), showing the anodes after 32 charge-discharge cycles, confirmed that the modified polymer adhered strongly throughout the battery operation even as the silicon particles repeatedly expanded and contracted. Tests at the ALS and simulations confirmed that the added mechanical properties did not affect the polymer’s superior electrical properties.

The new PF-based anode is not only superior but economical.

Using commercial silicon particles and without any conductive additive, our composite anode exhibits the best performance so far. The whole manufacturing process is low cost and compatible with established manufacturing technologies. The commercial value of the polymer has already been recognized by major companies, and its possible applications extend beyond silicon anodes.

—Gao Liu

This achievement provides a rare scientific showcase, combining advanced tools of synthesis, characterization, and simulation in a novel approach to materials development. The cyclic approach can lead to the discovery of new practical materials with a fundamental understanding of their properties.

—Zahid Hussain, the ALS Division Deputy for Scientific Support and Scientific Support Group Leader

Resources

  • Gao Liu, Shidi Xun, Nenad Vukmirovic, Xiangyun Song, Paul Olalde-Velasco, Honghe Zheng, Vince S. Battaglia, Lin-Wang Wang, and Wanli Yang (2011) Polymers with Tailored Electronic Structure for High Capacity Lithium Battery Electrodes. Advanced Materials DOI: 10.1002/adma.201102421

September 23, 2011 in Batteries | Permalink | Comments (29) | TrackBack (0)

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Very interesting potential solution to effectively deal with lithium anode swelling. If it can be mass produced at an affordable price within 5 years or so, it could become one of the first practical storage unit for highway capable BEVs with range competitive with current ICE vehicles. Let's hope that it will be mass produced in USA.

Okay, so this sounds like a really good development, and yes, not likely to result in cheap, revolutionary high-capacity Li-ion batteries in BEVs next year. That, however, is beside the point. Every new discovery in the field (and there have been lots of them) adds to the body of knowledge available to the folks in battery R&D, making it likely that BEV batteries will continue to significantly improve, in small or big steps, in the foreseeable future. Isn't that the way it always works?

And this new discovery happens to have been authored in the US. Hooray!

These incremental developments in battery systems will be increasing in frequency as the energy independence campaign accelerates. Notice the number of new tech battery solutions being announced. AND the new discoveries of petroleum and NG resources. AND breakthroughs in CHP appliance systems. AND H2 FC vehicles. AND infrastructure support for EVs.

ALL this happening in the face of a truly disturbing evolution in the LANR field:

http://www.nyteknik.se/nyheter/energi_miljo/energi/article3264361.ece

Andrea Rossi`s one megawatt cold fusion plant is nearly finished and ready for testing. Ouch. Talk about disruptive technologies!

Yes Reel$$...all energy produced by Andrea Rossi's cold fusion gadget will be stored into an ESStor unit and drive a BEV around for 100+ years.

"Composite anodes based on this polymer and commercial Si particles exhibit 2,100 mAh g−1 in Si after 650 cycles without any conductive additive."

If this means 10X present battery performance for 650 cycles(650,000 miles@ 1000 mi/charge) - manufacture, EV/energy problems solved.

If this is another "..if matching cathode developed" or deliberately misleading ".. after 32 charge-discharge cycles, the polymer is still tightly bound to the silicon particles, showing why the energy capacity of the new anodes remains much higher than graphite anodes after more than 650 charge-discharge cycles during testing.." - it sounds like fraud.

Right Harvey. But most people will want to update their vehicle around year 50 according to a recent study at the Algor Institute for Hazbins;)

No offense Al.

Anyone know of a site that tracks battery technology and discusses 'the state of the art'?

So many things appear as news items, but I can't string them together into a coherent story. I need a guru....

I would be a little leery of calling Rossi's project a gadget. I have been following the story since Jan. and at first thought it a hoax, but as time passes I am beginning to be a believer. (even tho Rossi is a bit flaky) There are several scientists that are beginning to be confinced. Of course if it is successful it will be several years to be of signifcance. Also when they say a megawatt plant they are reffering to a megawatt of heat not electriciy.( big differance)

"I would be a little leery of calling Rossi's project a gadget." - agreed.

In any case, it's claimed we will see the success OR failure next month, not in five or ten years.

"..after 32 charge-discharge cycles, the polymer is still tightly bound.." implies it isn't (tightly bound/functioning?) after 33+ cycles?

Reel is still touting Rossi, but won't take me up on my bet. It appears that he has much less confidence in Rossi than his posts would suggest.

Don't need your $ EP. But thanks for thinking of me! I just posted a link from a Swedish physics journal. How about critiquing the science Rossi's using?? Maybe NASA, MIT, CAL Tech, Naval Research Lab, and a dozen other LANR projects are all in "denial?"

http://www.cbsnews.com/video/watch/?id=4955212n

BTW, how does support for alternative energy help coal trolls??

Reel,

I haven't seen any links to NASA, MIT, etc espousing the technology yet, but I'd be glad to see them if you've got some links. And I mean real links they've published, not Rossi saying they did in yet another story.

That other link you posted has zero proof of anything and is nothing more than the writeups about more of Rossi's "flakeyness".

I did see some discussions with the labs who initially tried to verify Rossi's claims and they walked away from the table when Rossi refused to let them measure heat output from the unit.

Face it, we all wish Rossi had evented a new type of perpetual energy machine...but the chances are 99.99999999999999999999999999999999999999999999999% that he's just another flake. It's possible that he just doesn't know how to measure what he's got and so doesn't understand the real results, but if that was the case he'd allow independent verification. As it is, most evidence points to him being another swindler.

Sorry, those are just the facts on the table.

You know whats going to happen.. by bringing the equipment into the US it means that the NASA/Military/CFR/Chevron/GM/Aliens industrial complex will be able to bury and/or discredit the results.. this will prove to be a big mistake that will setback the human race another 100 years down the fossil fuel rathole.

LOL So bringing it into the US stops the Germans, the Chinese, the Indians, the Russians and anyone who does NOT have oil from using it?

Come on Herm, at least keep the conspiracy theories rationale.

What is sad about this is that every time someone comes out with "cold fusion" or EESTOR capacitors or now Rossi is that you'll never convince the fringe that magic simply doesn't work. The laws of physics have this nasty habit of being fairly consistent.

We all want to get off oil (except Exxon, Shell, BP,etc and their bought and paid for politicians of course) but we have to have a real alternative first, not unicorn farts.

"In my world, everyone's a pony and they all eat rainbows and poop butterflies"

Now, back to reality:

This is potentially a great advance. But as others have pointed out above...this is yet another great idea that may or may not be practical due to cost or some other factor that they may be sweeping under the carpet for now.

But it is encouraging that Berkley, NERSC, and NCEM have all had a hand in this so far and nobody is calling BS.

One of these breakthroughs is going to make it through the process in the next 4-5 years and give us a leap in battery tech...which one???

Watch the CBS story Dave... or are they part of your conspiracy to change the laws of physics??

http://www.cbsnews.com/video/watch/?id=4955212n

"The most interesting, and promising, at this point, in the farther term, but maybe not so far, is low-energy nuclear [LENR] reactions. This has come out of [22] years of people producing energy but not knowing what it is — and we think we have a theory on it. It’s producing beta decay and heat without radiation. The research on this is very promising and it alone, if it comes to pass, would literally solve both [the] climate and energy [problems.]" Dennis Bushnell, Chief Scientist NASA, Langley Research Center.

Oh, wait a minute - NASA??? THEY'RE trying to debunk the laws of physics too!

This isn't about you needing my money, Reel. It's about you standing up for what you say you believe in, with a commitment that means something.

You fail.

Sorry EP, I am quite happy with the facts I include in my posts. Cheap theatrics are unnecessary;)

Reel and Herm,

Look, I'd love for this to actually be true. But there is nothing to indicate it really is. It looks to be EXACTLY like what happened in the Cold Fusion mess. Take your CBS link Reel:

"Scientists today like to call it a nuclear effect rather than cold fusion. At least 20 labs working independently have published reports of excess heat - heat up to 25 times greater than the electricity going in"

This is EXACTLY what happened with Pons and Fleischmann and the original "Cold Fusion". They didn't realize it was just a chemical reaction. Hey, there's nothing wrong with that. It's how we get energy today...by burning things which is just a chemical reaction.

The question is will this "fuel" get used up quickly or not. It's possible and I'd LOVE to be proven wrong.

But for now, I'm with Engineer Poet on this one: I'll gladly bet you guys lunch and I travel all over the US and Europe so I'm sure I can find an excuse to come personally pay up if I'm wrong :-)

Sorry Dave... er, why is it we should believe you and not NASA, NRL, the Chairman of the Swedish Academy of Science’s Energy Committee?

Because NASA, NRL, et al. didn't say what you claim they said.

Imagine what a mini cold fusion box coupled with a mini-ESStor super-cap unit could do for electrified future vehicles. Unlimited range and the surplus energy could supply all power needed for large home and the neighbors fleet etc.

All oil producers, refineries, gas stations, coal mines and power generation plants could close shop?

Come on Harvey, it would be KAOS! Cats and dogs sleeping together! But I'm gonna buy some Orville Redenbacher stock just in case.

And Engineer-Poet, might I suggest you consider the following:

http://www.gamblersanonymous.org/ga/index.php

I only bet on sure things, Reel. Like that out of every 3 assertions you make, 2 are certain to be wrong.

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