PNNL Develops Hybrid Anode That Could Extend Lithium Sulfur Battery Life

JAN 15 2014 BY MARK KANE 22

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Lithium-Sulfur Li-S batteries are probably one of the most promising future energy storage devices that could enable electric vehicles to drive much further on single charge.

Pacific Northwest National Laboratory is one of many scientific centers developing a new concept for such cells and recently released an article on a new “hybrid” anode material that increases the poor basic cycle life of Li-S from 100 to over 400.

PNNL Laboratory Fellow Jun Liu, who is the paper’s corresponding author, wrote:

“Lithium-sulfur batteries could one day help us take electric cars on longer drives and store renewable wind energy more cheaply, but some technical challenges have to be overcome first. PNNL’s new anode design is helping bringing us closer to that day.”

400 doesn’t sound like too much (especially when we’ve seen articles with higher values) but we must remember that, at 2-3 times the energy density of current lithium-ion cells, Li-S packs could have extremely high capacity, which means they’d be cycled less often.

400 is not the maximum performance, because the tested cell lost just 11% of initial >800 mAhg−1 capacity at a fair current of over 2 C (1,737 mA g−1). 2C means charging (or discharging) in half hour. At lower currents, capacity can be even higher and capacity fade lower.

“The lithium-sulfur battery’s main obstacles are unwanted side reactions that cut the battery’s life short. The undesirable action starts on the battery’s sulfur-containing cathode, which slowly disintegrates and forms molecules called polysulfides that dissolve into the battery’s electrolyte liquid. The dissolved sulfur eventually develops into a thin film called the solid-state electrolyte interface layer. The film forms on the surface of the lithium-containing anode, growing until the battery is inoperable.”

“Most lithium-sulfur battery research to date has centered on stopping sulfur leakage from the cathode. But PNNL researchers determined stopping that leakage can be particularly challenging. Besides, recent research has shown a battery with a dissolved cathode can still work. So the PNNL team focused on the battery’s other side by adding a protective shield to the anode.”

“The new shield is made of graphite, a thin matrix of connected carbon molecules that is already used in lithium-ion battery anodes. In a lithium-sulfur battery, PNNL’s graphite shield moves the sulfur side reactions away from the anode’s lithium surface, preventing it from growing the debilitating interference layer. Combining graphite from lithium-ion batteries with lithium from conventional lithium-sulfur batteries, the researchers dubbed their new anode a hybrid of the two.”

“The new anode quadrupled the lifespan of the lithium-sulfur battery system the PNNL team tested. When equipped with a conventional anode, the battery stopped working after about 100 charge-and-discharge cycles. But the system worked well past 400 cycles when it used PNNL’s hybrid anode and was tested under the same conditions.”

Liu remarked:

“Sulfur is still dissolved in a lithium-sulfur battery that uses our hybrid anode, but that doesn’t really matter. Tests showed a battery with a hybrid anode can successfully be charged repeatedly at a high rate for more 400 cycles, and with just an 11-percent decrease in the battery’s energy storage capacity.”

Another promising but information is on Coulombic efficiency of more than 99%, which is on the level of lithium-ion cells.

Hopefully, someone will soon try to commercialize one of the Li-S cell designs for EVs.

Source: PNNL via Green Car Congress

Categories: Battery Tech

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22 Comments on "PNNL Develops Hybrid Anode That Could Extend Lithium Sulfur Battery Life"

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Li-S is the next battery step change, with commercialization in 2016. The benefits are a much lighter weight cell – about half the weight of today’s Li-Ion NCA cells (500Wh/kg instead of 250). But they have about the same energy per unit volume (around 600Wh/l), so while they weigh half of current cells, the still take up about the same volume in space.

This means EVs will need to be designed to be EVs from the ground up (like the Tesla) and not just an ICE car retrofitted with a battery pack eating up trunk space. But the weight reduction will make EVs more efficient because instead of 500 or 1000 lbs of battery cells, its half that, improving MPGe. On a Nissan Leaf, that’s around 250 lbs, and on a Tesla is around 500 lbs (85kWh). How much farther would a Tesla go on the same battery if you cut 500 lbs off the curb weight?

Anthony,
What is your opinion on using Li-S as a secondary battery to be used as an extender?

No real use – you’re just better off using 100% Li-S rather than 80% Li-S and 20% regular Li-Ion.

They will have similar enough characteristics when it comes to charging, discharging, cycle and calendar life. Plus, Li-S will be cheaper than current Li-ion at similar volumes (some companies are touting $100/kWh but I’ll believe that when I see it).

No, different battery types can make sense. Some batteries can do much higher charge/discharge rates. Having hundreds of thousands of regenerative braking microcharges go to long life cells can be useful, too.

There have been some supercapacitor breakthroughs that make me think having 0.5-1 kWh of them could be quite cheap and not only do more efficient capture of braking energy, but let you release that energy in a 500kW burst, making an EV an absolute rocket even if the main pack was only 20kWh.

I’m sorry, I don’t believe in Santa Claus, the Easter Bunny, or sufficiently energy dense supercapacitors suitable for EVs.

(flame suit on)

I believe Tesla’s cells are only good for around 500 cycles. But, as mentioned already, the large capacity means they don’t get cycled nearly as much. So, at 3 times the energy storage, that would give my Leaf a range of well over 200 miles. With that sort of range, it would take me quite a while to cycle them 400 times. That would essentially be 80,000 miles. And here’s a question. How long will the batteries last after the 400 cycles? For example, if the batteries lost 50% of their capacity, the Leaf would still have 100 miles range. Still pretty darned good!

Why do you believe Tesla’s cells are only good for 500 cycles?

I read that somewhere on an article comparing the types of batteries used by Nissan, GM, and Tesla. Sorry can’t cite the source right now.

This article regarding the LiNiO2 chemistry Tesla uses suggests it might retain as much as 82% of its capacity after 5000(!) cycles.

http://mtrl1.me.psu.edu/Document/ZhangY_JES_2009.pdf

Panasonic put out a paper showing that they can do 3000 cycles (albeit only cycled between 4.05V and 3.6V) with minimal degradation, even at elevated temperature:
http://ma.ecsdl.org/content/MA2011-02/17/1282.full.pdf

Tesla has said their batteries are customized for vehicle use. You probably got your data from Panasonic’s regular NCR18650 datasheet.

But you make a good point about reduced range still being useful. Older cars are generally driven less, as are second/third/fourth cars in a household:
http://cta.ornl.gov/data/tedb32/Edition32_Chapter08.pdf

Yes they lose 10 to 15% After 500 cycles, the roadster over 100K miles had loss and average of 15% battery capacity. This means the cycle of Tesla MS battery is around 10 years, however you still have around 200 miles rage fora 1000 cycles more before drops below 70% capacity.

I am encouraged to see progress by a member of Argonne’s JCESR project. It is also interesting to see they are still working with Lithium after their Director said the direction would be to pass beyond Li to using metals with 2 and 3 outer electrons, i.e., Mg and Al. Perhaps this is an interim step to prove the sulfur cathode before moving on to Mg and Al anode experiments.

What most battery breakthrough announcements have in common is that they are made by Asians. What all battery breakthrough announcements have in common is that they never result in a product.

Tell me about it. I am not sure I agree with the first part (about the Asians) as there have been plenty of USA firms claiming battery breakthroughs. However, I definitely agree with the second part. 99.99% of them never become a real product.

@ David Murray: More precisely: people with Asian names, yet no doubt often US nationals as this Jun Liu fellow mentioned in this article probably is. Also not 99,99%: 100%. If it were less some sort of miracle battery would be available by now but there isn’t and I don’t think there will be until the oil runs out.

You can’t say 100% because the batteries we are using in cars now were considered breakthroughs at one point or another.

Fair point but although current battery tech is substantially better than older technology it’s still nowhere near what I would consider the “miracle battery” that could make electric motoring mainstraem.

+1

Never is a really long time. All these new battery technologies are fighting one thing. Corrosion build-up on the cathode. From what I understand this is the issue that eventually kills all batteries, but at different rates. It appears to be a fact of life that the smart guys figure out how to mitigate to an acceptable level. Liu isn’t promising anything. He is banging his head against the same wall that the aluminum-air researchers are, appropriately showing his work and disclaiming expectations. One can believe that they will “never” solve this problem. Or one can wonder “how” they are going to mitigate this problem to a level that justifies production. Since the problem didn’t kill the usefulness of NiCad or nimh or Li-ion, it won’t kill the next thing either. We dummies just don’t know whether that next thing will be Al-air, Li-S or something else. This article just introduces us to some details about Li-S in case it is the next thing, or leads us to the next thing. You have to appreciate the fact that teams of the people on the other end of our product purchase dollars are researching everything that shows any potential at all.

Funny you point that out, but it’s true, Envia is founded by Asians, so is A123….but not sure about those flow oxide type though….

Many of the younger engineers and scientists working on all kinds of new technology are from Asia, not just batteries. There are likely multiple explanations for that. First, there are a lot of people on this planet with Asian names. A lot of battery research is done in countries where most batteries are manufactured such as South Korea and Japan. Many battery startup companies in the U.S. hire talent from U.S. universities that have a high percentage of students who came from Asian countries. This is because of the high reputation of U.S. colleges built up due to lavish engineering and science funding during the Cold War. Also, foreign students generally pay much higher tuition and make money for the schools. Also, many U.S. born students with non-Asian names choose to study (easier?) topics other than engineering, math, and hard science. Those are pretty good reasons why many battery research papers and announcements feature people with Asian names. But, you claim that 100% of the battery “breakthrough” announcements that don’t result in real products are by people with Asian names. Have you done or found any objective research to back up that extraordinary claim? If it’s too hard to do,… Read more »

Great article Mark. I got it late cuz I’m on vacation in Mexico.