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surfingslovak
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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 1:30 pm

GregH wrote:
drees wrote:Somewhere around 3.75V resting voltage (~360V pack voltage) or around LBW would be a good suggestion for the LEAF, but realistically, anything between VLBW and 80% is good enough for short term storage. For longer term ideally you'd want somewhere between LBW and 40% and to keep it as cold as possible.

But not VLBW (24 Gids)? Not 10-15 Gids?
If not, why not? (with respect to battery longevity)
Image

A friend of mine sent me this video. Loved it. Especially the term "sausage factory". I wish this video was available when we were painstakingly putting a knowledge base for this battery chemistry together. I'm not aware of anybody in the industry, who would be doing anything even remotely similar. No wonder that one of his graduates is leading battery testing at Tesla. I think this also settles a lot of the debates we had in the days past. It's amazing how high emotions were flying at the time.

In terms of degradation and capacity loss at low stage of charge, please look up the Jahn-Teller effect. I referenced it here on the forum a few times, and if memory serves, these are rather slow crystalline changes, which attack the spinel structure of the LiMn2O4 cell. Also, I believe that the Nissan LEAF manual states, that the battery should not be left at a low state of charge (think turtle mode) for more than two weeks. This would further corroborate that degradation processes at very low state of charge progress slowly.

With regards to the chemistry tweaks Nissan performed, it appears even more likely that those were predominantly electrolyte changes.
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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 1:59 pm

palmermd wrote:
GregH wrote:
drees wrote:[*]The lower the SOC the battery is charged, the longer it will last (example was storing battery at ~20% or 3.5V resting voltage).


IIRC (and my recollection is foggy at best).. low voltage degradation is at extremely low voltages (0-2V) and not any voltage a Leaf battery would ever be allowed to see (3.0-3.5V.. although I have seen screenshots showing 2.7xV)
So I guess my question would be: Is it ANY worse (for battery longevity) to leave a Leaf sitting at 3.5V (say, 10-12 Gids or so) than at 50% SOC?


The battery he mentioned sitting at 3.5v for 5 years was not necessarily a Leaf battery chemistry. In fact odds are it was not. His point was that he had a battery sitting at 20% SOC (which was 3.5v for that particular battery) and after all that time in a non temperature controlled situation the cell appeared to be "new" for all practical purposes.

Yes, we debated this a while ago, and the consensus was that storing the LEAF at about three battery bars was best for longevity. We did not have any means of quantifying that benefit, but now we know, thanks to Prof. Dahn.

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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 2:01 pm

Weatherman wrote:Unfortunately, for the LEAF's battery, the degradation rate appears to be so overwhelmingly affected by the number of hours the battery temp spends above 25C (77F), that nothing else matters very much. Of course, increasing the temp to 30C or 35C just makes things worse.

Indeed. I know 2013 owners who claim that their battery is degrading much slower, all other things being equal, which would suggest an electrolyte tweak. Likely an additive or two, according to Prof. Dahn's lecture.

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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 2:04 pm

ericsf wrote:On the negative side, the existence of the "other" failure mode, the catastrophic one was news to me. The degradation we're all talking about for the LEAF is the gradual one. What about the catastrophic one, does anyone know what should be our expectation about that?

Yes, we talked about it, but nobody could tell for sure. Since Nissan is offering a 100K warranty, a catastrophic failure should be covered. Accelerated cycle testing is easily doable, and one would hope that they have done at least that, even though their calender life testing was apparently wanting.

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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 2:06 pm

palmermd wrote:Right at the beginning. Starting around 3:35. At 5:00 more detail and at 5:30 he shows that slow charging and discharging at temperature kills cells. He continues to about 7:20.

Not necessarily. I have seen other studies, which suggested that as well, but the effect was only visible later in life. The same study suggested that C/2 charging was best in the long-term, and we assumed that this was because of the much shorter charge time, and likely less heating overall. L1 could be still OK, if it's not used exclusively and for 100s of cycles.

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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 2:38 pm

RegGuheert wrote:
ericsf wrote:He mentions 2 different type of chemistry for the LEAF and the Volt. A good one and a bad one when it comes to resistance to heat. He says it's a 50/50 blend. Li(NiMnCo)O2 and LiMnO2.

Does anybody have any info on this? Does Nissan blend the 2 type of chemistry in each pack or do they produce 50% with one type and other 50% with the other. Or could he be referring to the new "hot climate" battery chemistry? But in that case why would he say it's 50/50 instead of old/new and why did he throw the Volt in the same basket?
I'm pretty sure he was talking about the chemistry of the anode and the chemistry of the cathode when he said that. He is discussing the combination of those two chemistries in general, but likely without any knowledge of the specific additives used in the electrolytes of either the batteries made by Nissan or LG Chem (for the Chevy Volt).

To my knowledge, there is no cobalt in LEAF's battery pack. It's a manganese spinel cathode. Initially, it was assumed that it's pure LiMn2O4, but later it was revealed that the cathode was a blend. I forget of what, but definitely no cobalt. The Volt and the LEAF are pretty close in terms of the chemistry used, that much we knew already. We just did not have any way of quantifying their behavior, aside from the data painstakingly gleaned from the field. Prof. Dahn's method is much more accurate. The basis electrolyte is the same in both vehicles, but they very likely differ in terms of additives. Also, the Volt uses a hard graphite anode, whereas the LEAF does not. Prof. Dahn has seemingly confirmed that. This should further help longevity.
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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 5:38 pm

a similar thread has also been started on the Tesla board with correspondence with the Professor... pretty interesting stuff! http://www.teslamotorsclub.com/showthread.php/27109-Why-do-Li-ion-Batteries-die-And-how-to-improve-the-situation
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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 5:55 pm

surfingslovak wrote:To my knowledge, there is no cobalt in LEAF's battery pack. It's a manganese spinel cathode. Initially, it was assumed that it's pure LnMnO2, but later it was revealed that the cathode was a blend. I forget of what, but definitely no cobalt. The Volt and the LEAF are pretty close in terms of the chemistry used, that much we knew already. We just did not have any way of quantifying their behavior, aside from the data painstakingly gleaned from the field. Prof. Dahn's method is much more accurate. The basis electrolyte is the same in both vehicles, but they very likely differ in terms of additives. Also, the Volt uses a hard graphite anode, whereas the LEAF does not. Prof. Dahn has seemingly confirmed that. This should further help longevity.


The electrode contains Li-Mn-O spinel and Li-Ni-O, but I don't know the exact composition. NEC, Nissan's partner, has reported some of their results: NEC Technical Journal, Vol. 7, No.. 1, 2012.
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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 5:59 pm

surfingslovak wrote:To my knowledge, there is no cobalt in LEAF's battery pack. It's a manganese spinel cathode. Initially, it was assumed that it's pure LnMnO2, but later it was revealed that the cathode was a blend. I forget of what, but definitely no cobalt. The Volt and the LEAF are pretty close in terms of the chemistry used, that much we knew already. We just did not have any way of quantifying their behavior, aside from the data painstakingly gleaned from the field. Prof. Dahn's method is much more accurate. The basis electrolyte is the same in both vehicles, but they very likely differ in terms of additives. Also, the Volt uses a hard graphite anode, whereas the LEAF does not. Prof. Dahn has seemingly confirmed that. This should further help longevity.


2011/12 Nissan LEAF cells cathode was 82% Mn2O4 18% NCA blends
blending Nickel oxides with Manganese Spinel workes similar to adding a beneficial electrolyte addictive.
blending Manganese Spinel to Nickel cathodes also works similar as adding a beneficial electrolyte additive.
ie each way is beneficial for improving longevity. Complementary cathodes for blending

US spec 2013/14 have further electrolyte additive, along with electonic changes and unknown supply crossover dates, so its not easy to compare or expect them to have similar longevity. NEC docs suggest an increase of 300% life in hot climates, but only 50% increase in life in cool climates as a possible option.

Cell durability for Manganese based battery has a wide wide range of possibilities, even small tweaks can have a large effect, but it takes time to validate/implement them.

Volt's LG cells are significantly different to Ford's LG cell.

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Re: Why do lithium batteries die and how to improve them?

Sun Feb 09, 2014 8:55 pm

GaslessInSeattle wrote:a similar thread has also been started on the Tesla board with correspondence with the Professor... pretty interesting stuff! http://www.teslamotorsclub.com/showthread.php/27109-Why-do-Li-ion-Batteries-die-And-how-to-improve-the-situation


Here is the professors response to an email (from Tesla forum, so you don't have to read the whole thread):

"Thanks for this e-mail. I have placed responses within your text using CAPS (not yelling) but so you can find my responses


Jeff Dahn, FRSC
Professor of Physics and Atmospheric Science
NSERC/3M Canada Industrial Research Chair
Canada Research Chair"

"Since electricity appears to have become the defacto currency for renewable energy and I have a great interest in and now investment in renewable technologies (own a Nissan Leaf and Tesla Model S and a 9.8 kW PV system), I have been doing my best to learn whatever I can about energy storage and how batteries work, in particular, the way end user habits effect overall life.

THIS IS AWESOME.

I am wondering if your research has revealed what the best way to extend a batteries life is. I have concluded, as you have noted, that high ambient temperatures degrade these batteries the most. Living in Seattle, we are blessed with a moderate climate so I feel pretty fortunate in that regard.

ABSOLUTELY. AVOID HIGH T WHENEVER POSSIBLE.

Debate continues on whether charging habits will turn out to have much effect on battery life. I have started leaving all of my li-ion consumer products at about 50% charge when they are not in use. Tesla makes this very easy with a battery slider that allows the consumer to choose between 50% and 100% end charging and even has this feature integrated into the phone app to make it very easy to adjust upwards on the fly as long as the car is plugged in. I have installed an 80A (20 kWh) charger so that I can quickly add charge to the Tesla S, allowing me to minimize the inconveniences associated with leaving the pack at a low state of charge and thus increasing the amount of time the battery stays at a mid/low SOC. I tend to do mid pack cycling, discharging generally between 30 and 70% when convenient, while aiming to have the car sit for the longer stretches like overnight, at 50%. I'm not religious about this, just tend to aim in this direction generally.

I THINK THAT IF YOU ARE KEEPING THE CELLS BELOW 4.0V (NO WAY FOR YOU TO TELL THAT, HOWEVER) THE BATTERY LIFE WILL BE VERY IMPRESSIVE. WE ARE TESTING CELLS BUILT IN 2002 THAT HAVE 2002 TECHNOLOGY (LIFETIME IS BETTER NOW) THAT STILL HAVE 75% OF THEIR INITIAL CAPACITY (CYLCED AT 37c THE WHOLE TIME). THESE CELLS WERE CHARGED ONLY TO 4.075V. MODERN CELLS LIKE THOSE IN TESLA CHARGED TO 4.0V SHOULD LAST A FEW DECADES, I SUSPECT, WITHOUT ANY ISSUE (SO KEEP YOUR CAR FROM RUSTING!). WHERE IS 4.0V RELATIVE TO STATE OF CHARGE? MAYBE 75%.

ONE OTHER THING I WOULD RECOMMEND IS TO AVOID HIGH RATE CHARGING AT TEMPERATURE BELOW 0C. ESPECIALLY WHEN THE CELLS ARE ABOVE 75% SOC. TESLA ELECTRONICS MAY PREVENT THIS

In your opinion, do you believe it is worth the effort to keep li-ion batteries at 50% or thereabouts for the bulk of their resting time to extend their long term capacity and if so, do you have any idea how much of a difference this is likely to make over say a 8-15 year time period.

KEEPING BELOW 4.0V MAY DOUBLE OR TRIPLE LIFE TIME COMPARED TO A FULL CHARGE EVERY CYCLE, I SUSPECT.

Also, given that Tesla limits power to the motor during extremes, like high and low charge and high and low temperatures, is there really any reason to avoid running the battery low, assuming Tesla doesn't let you discharge the battery all the way anyway and limits discharge rate as the charge level drops. I assume running the battery to zero (of what the manufacturer allows) does little to the overall life as long as it gets recharged soon after. I assume that low and high states of charge are more an issue if exposure is prolonged, is that correct?

I THINK THAT REALLY DEEP DISCHARGE SHOULD BE AVOIDED AS THEN THE GRAPHITE EMPTIES OF LI AND THE CELL POTENTIAL RISES TO THE POINT WEHRE THE SEI ON THE GRAPHITE SIDE CAN BE DAMAGED. KEEP THE CELLS ABOVE 3.0V PER CELL (NO WAY YOU CAN TELL THAT) BUT THAT WOULD BE ABOUT 98% DISCHARGED. SO DO NOT DISCHARGE BEYOND 98%.

Any opinion you may have on this subject will be much appreciated in helping me understand what the limits of this technology are and how to best treat the batteries in my cars and consumer products.

THE TECHNOLOGY IS REALLY PRETTY AMAZING WHEN YOU THINK OF IT. "

Here is his response to follow-up email:

Again - my responses are in CAPS below


Jeff Dahn, FRSC
Professor of Physics and Atmospheric Science
NSERC/3M Canada Industrial Research Chair
Canada Research Chair

Subject: Re: Question RE: "Why do Li-ion Batteries die ? and how to improve the situation? "

Professor Dahn, if you have a chance, I have a few more follow up questions. I do very much appreciate your time answering my questions!

Since they are both cobalt based would the consumer care recommendations (store at lowish SOC, Lowish temperatures, tending to mid voltage cycling) for LiCo02 cells be the same as a LiNiCoAi02 or a LiCoAi02 cell?

YES

Also, does the rate of charge (0.5C vs. 1C vs 1.5C etc.) have any impact on the cell life?

YES - I WOULD AVOID CHARGING AT GREATER THAN C-RATE AND WOULD RECOMMEND C/2, ESPECIALLY FOR "ENERGY CELLS". POWER CELLS (E.G. IN TOOLS) WILL HAVE LITTLE PROBLEM WITH C-RATE CHARGING AND WOULD BE FINE. THE CELLS IN THE TESLA S ARE MORE AT THE ENERGY CELL END OF THE SPECTRUM.


have you tested NCA cells like the Panasonic NCR18650A and NCR18650B and would their care characteristics be the same.

WE HAVE LOOKED AT THE "A" AN IT IS VERY SIMILAR TO LCO CELLS

Nicad is less and less common in consumer electronics but is still used and I have several gadgets that have them. I have been treating these pretty much the same (store at lowish SOC, Lowish temperatures, tending to mid voltage cycling) accept every so often I do a complete discharge and full charge to reduce the tendency toward memory effect. In your opinion, is this on track? anything to add?

THIS IS GOOD. MEMORY EFFECT COMES WHEN CELLS ARE LEFT FULLY CHARGED OR FLOATED AT FULL CHARGE FOR LONF PERIOS OF TIME.

In general, I am amazed at how few of devices/chargers have any sort of BMS other than avoiding runaway combustion. It would make so much sense for every one of these devices to have a long life mode, where they could be left plugged in but only charge to about 50%. so many of these devices end up plugged in all the time, and it dramatically cuts down their shelf life. please consider explicitly recommending this in your research if appropriate. To many phones, computers etc are thrown away because the battery only lasted a year or two, when, if treated better, could have lasted 5-10 years. by applying this care regimen, peak performance of many products can be vastly extended. I've gotten 5 years out of an iphone, 5+ years out of a cordless shaver and long life out of many other products. This has required a lot of careful charging... it would be so much easier if I could set the SOC limit on each device based on my needs, such as at home near a charger vs traveling where I need max charge. we need someone like you to push the industry to make this kind of thing a standard! (no pressure :~). Tesla with it's slider option has nailed this. some way to adjust the end charge limit should be on all consumer products. a SOC meter that showed red at both ends, with green in the middle, would help this be more intuitive for consumers, who now simply think fully charged is the best, which simply leads to killing the battery prematurely.

THIS WOULD BE A GOOD THING. MOST HUMANS TREAT BATTERIES A BLACK BOXES AND DO NOT THINK OR CARE. YOU ARE A RARE SOUL!

OH and as an aside, the Tesla S is aluminum, so no need to worry about rusting :~) and the AC induction motor is brushless with the only contacts points being two bearing sets... potentially, this car should last a very long time!

I KNEW ALL OF THIS AND BRIEFLY FORGOT! "
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