Long term storage of Li-ion batteries?

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BrianK
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Long term storage of Li-ion batteries?

What would the voltage be for a typical 18650 Li-ion cell at 40% charge, for long term storage, unused, in the refrigerator?

40% is the recommended state for long term storage, correct?

Too, does storage in a freezer stop the aging of Lion primaries as it does with alkaline and carbon?

Edited by: BrianK on 07/04/2016 - 09:32
semiman
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Very close to stopping it. Most 18650 will be rated for -20C storage (or colder), but not all of them so be careful. Your freezer will get close to -20C.

Always allow time for warming, and condensation to evaporate.

mapache
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Hi Brian, have a read of Lithium-ion battery safety 101 it will tell you everything you need to know and more.

I usually store my 18650s at 3.8v

BrianK
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Thanks; I read the battery safety thread but missed the storage voltage. I saw it this time through. Duhhh! On me. Smile

Last I checked my freezer it was -20F, so that’s out. That leaves my refrigerator out in the shop which I keep very close to 32°F

CRX
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Maybe stored in a sealed container in the fridge cooler compartment, not the freezer i would think.
I store mine at around 50% measured cell capacity as cell voltage can differ between cells.
Anywhere between 40 – 60% is cool LOL for long term storage. I use 50% to allow for some self discharge which may be more prevalent in protected cells.

HKJ did some testing on this

Estimating Remaining Capacity in Li-Ion Cells

BrianK
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Thanks!

If I’m understanding that chart it appears that different brands and models of batteries can have wildly different capacities at a chosen voltage. If I decide to store a battery at 3.7 volts it could be almost dead and others would be fine. That complicates matters doesn’t it?

Mountain sells this charger: http://www.mtnelectronics.com/index.php?route=product/product&path=79&pr...
Would it tell me what I need to know for proper storage of the batteries? Or is it just to be a crude representation of capacity and not usable for this*? BTW, I have a DMM to check voltage. Or am I just making more of this than it needs to be?

*Implied in that question is another… is there an easy way to check capacity? Again, am I making more of this than I should?

My problem is that I have far too many batteries and I can’t see leaving them out to degrade rapidly if I don’t need to use them. My experience with Nimh batteries didn’t do so well when moving to Li-ion batteries. These things last close to forever before needing a charge in my normal use, and I use them every night. Before anyone writes something… no, I’m not taking them too low before charging. At least not by DMM. But if that charger (above) actually is accurate it might be a better guide.

Budda
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I use my MC3000 that discharge the li ion at 3.7 volt for storing purpose.

However the fridge thing make sense IMHO if you have a lot of batteries.
If I have to start worrying about the li ion in the fridge (did someone put oil on them? or added to the salad?), and their humidity/rust, it has to be for some expensive battery.
Today you can buy cells for less than 4€ each, and remember that every year that passes the cells you have in the fridge will still decay, while the ones you can buy should be not only new, but also with improved performances due to constant research.

Here are all my reviews on BLF

CRX
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That charger (VC2) doesn’t have a discharge function, which is the only real way to determine capacity.
It shows how many mAh is put into the cell, which does give a fair guide on healthy newer cells but maybe not so much on older ones.

3.8v should be a fine rested measurement for storage of cells though.

Don’t worry about it too much, you’ll be wanting to replace cells every 3-4 years anyway.

Maybe the Opus BT-C3100 V2.1 would be better for you.

BrianK
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Thanks guys. Looks like I’ll be getting that Opus charger.

Yeah, noobs do stuff that just doesn’t make sense! OK, I’m discussing myself. I didn’t have a clue, but I don’t want to just destroy these batteries either. I simply don’t need so many charged batteries.

sidecross
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I live in an earthquake and fire danger area and I keep all my 18650 and 26650 batteries charged and check them every three months with a static voltage measurement. Batteries are stored in a cool, dark, and dry environment.

I have been following this procedure since 2012 without problems. From my reading and listening to people on lithium ion battery safety and battery efficiency there is no absolute method for storage.

What is needed is an evaluation of battery needs and requirements without regards to the time and external power needed to charge lithium ion batteries.

“You must have a plan, if you don’t have a plan, you will become part of someone else’s plan.” Terence McKenna

Zebretta
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Budda wrote:
I use my MC3000 that discharge the li ion at 3.7 volt for storing purpose.
CRX wrote:
That charger doesn’t have a discharge function, which is the only real way to determine capacity. It shows how many mAh is put into the cell, which does give a fair guide on healthy newer cells but maybe not so much on older ones. 3.8v should be a fine rested measurement for storage of cells though. Don’t worry about it too much, you’ll be wanting to replace cells every 3-4 years anyway. Maybe the Opus BT-C3100 V2.1 would be better for you.

Old thread…but still relevant and came up in Google today while searching on “Storage of Lithium batteries”

Didn’t HJK say the MC3000 is by far the more versatile charger?
I have one…it most certainly does have a Discharge function and also Refresh, Cycle and many other customizable functions.

Oh, here it is…..

HKJ wrote:
The SkyRC is the most flexible and precise charger on the market. To improve precision people with precise equipment can calibrate their own chargers very easy.
The first batch had one hardware issue (Sometimes a pin breaks inside). At the same time this was fixed the fan was also turned around, this improved the cooling, before that the charger had to automatic reduced the discharge rate to avoid getting too hot.
The software has been updated a couple of times, but all the basic functions works in all software versions. The newer versions has fixed some obscure details and added a lot of new stuff to the charger. Because the software is user upgradeable all owners of the charger can upgrade the charger.

Opus and Dragon is nowhere near the functionality and precision of the SkyRC charger.

CRX
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Of course the MC3000 is far more versatile . I was refering to the VC2 BrianK linked, not the MC3000 Wink

Overmind
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I store them fully charged at around 16 C.
The temperature is good and requires nothing to keep it there.
Storing them fully charged may not be the officially recommended practice, but that way I can quickly detect in time if any of them have problems (voltage drops significantly instead of just a little over a long period).

hank
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Quote:
I live in an earthquake and fire danger area and I keep all my 18650 and 26650 batteries charged and check them every three months

Same here. I suppose keeping my Go-bag in the refrigerator might slightly improve their longevity, but I can live with recycling and replacing cells every three or four years. I already have to do that with the alkaline cells.

Helios azimuth
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Most everyone says to store at cool temperatures, but this was on the web months ago:

“Lund Instrument Engineering: July 19 2018. https://www.powerstream.com/Storage.htm:
Cadex’s recommendations are to store below 15° C (59 F) at 40% of full charge…. Our experience is that with cells stored at room temperature for 3 years that the non-recoverable capacity did not decrease, so this is probably manufacturer dependent.”

I am not sure about the wording there, but assume they meant to say they could recover capacity about the same as with the Cadex recommendation? Anyway, after reading that my extra refrigerator space has been dedicated to beer, LOL. But each to his own, do whatever seems right to you.

docware
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Calendar aging strongly depends on time, SOC and temperature.

Helios azimuth
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Thank you, docware for the info.

Apparently another factor is manufacturer (chemistry) since they seem to have said they had good experience with their batteries (Panasonic if I remember correctly) after 3 years at room temperature. Some of the information on the web is not dated and we seldom know the latest manufacturing schemes, but we can hope quality is improving with added research. Do you know what years the graphs you posted represent and the battery or batteries tested?

Still, the statement I quoted was removed from their website, so it might not have been totally accurate. I am not trying to argue, but just find cell data to be hit and miss. That is one of the reasons BLF is so useful, so thanks to all who share their analysis of lights and cells.

docware
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The study is dated 19.4.2017, cells are Panasonic NCR18650PD. You can read the whole study here :

https://mediatum.ub.tum.de/doc/1355829/file.pdf

Calendar aging – page 43 till page 71.

Different chemistry, manufacturer, electrolyte additives, ….. may have little bit different results, however the statement from this study is in general valid for all cells : calendar aging strongly depends on time, SOC and temperature.

Phlogiston
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Thanks for the link, docware, I’ve saved a copy of that Thumbs Up

Helios azimuth
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Yes, thank you. Very informative study.

The graphs you show and the ones on page 69 seem to indicate storage at 10C (50F) and 25C (77F) might be acceptable depending upon ones needs. It is very high temperatures and high SoC that are problematic. Cells stored at 3.7V for 15 years are thought to exhibit a capacity fade of 6% at 10C and not quite 10% at 25C. Maybe this is why Lund Instrument did not find temperature to be a major problem for 3 years. Since I do not intend to store my batteries for 15 years, the beer wins the extra space in my refrigerator, not my batteries.

Stored at 4.1V at 25C they are estimated to lose 16% capacity in 15 years, which is much better than one would think. But it is not inconvenient to store at lower voltage, so that is where I will focus.

Please correct me if my thinking is in error and thanks again for providing the study. It can help anyone can see the impact of various factors on their storage decisions.

docware
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Generally for long term storage is better lower temperature as well as lower voltage. Definitely recommend to use voltage bellow 50 % SOC which is bellow 3,7 V for majority of the cell. Good to remind that all producers from BIG FOUR (Panasonic/Sanyo, LG, Samsung, Sony) are sending their products to distribution at 3,5 V. Values in the chart are informative only, not absolute numbers, especially at low SOC end :

Kame Sennin
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Helios azimuth wrote:
… the beer wins the extra space in my refrigerator, not my batteries ...

I love this forum Smile

Helios azimuth
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Helios azimuth wrote:
Stored at 4.1V at 25C they are estimated to lose 16% capacity in 15 years, which is much better than one would think.

This very informative study shows a higher degradation of their NCA cathode material at higher voltages, leading to increased internal cell resistance. Don’t have time to look it up now, but it is in the study. Sorry, I read that and then forgot it before my last post.

And thanks for the chart, it is quite helpful. This is real information; I appreciate this forum too.

WalkIntoTheLight
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Yes, excellent information. I’m curious to know what long-term effect is on internal resistance. i.e, are high-discharge cells still good for high-discharge after 15 years, even when the capacity is still good?

Helios azimuth
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WalkIntoTheLight wrote:
Yes, excellent information. I’m curious to know what long-term effect is on internal resistance. i.e, are high-discharge cells still good for high-discharge after 15 years, even when the capacity is still good?

Good question. This study utilized Panasonic NCR18650PD cells with the highest discharging current presented in the data sheet of 10 amps (page 16 of the document). There might be differences with other batteries, or maybe not much, I would not know. They did not test high discharge rates in this study. Let us know if you find out.

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Concerning the difference in cells from different manufacturers (and the same cell from the same manufacturer produced later) the study sheds light on the changing landscape:

The cells were all of the same type but stemmed from two different production lots. The cells from the first lot were used in the first calendar aging study and in the cycle aging study on driving operation; the cells from the second lot, produced about six months later, were used in the second calendar aging study and in the cycle aging study on charging protocols….
As these cathodic side reactions are not observed in the second study, it is assumed that slight changes in the functional materials, such as modifications of the electrolyte and its additives, have reduced the cathodic side reactions of the cells examined in the second aging study, which were produced several months later.