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Lithium-Ion battery degeneration
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gueston:

--- Quote from: Siwastaja on September 02, 2020, 02:07:39 pm ---
--- Quote from: gueston on September 01, 2020, 07:20:29 pm ---But I can also see that the charging is regulated with the /CE pin, which I can control from the software. In that case I can control and keep the charge between 40-60% if I detect a constant connected power source. Am I right with this approach?

--- End quote ---

That would create a lot of alternating charge-discharge cycles between 40%-60%. Likely the cell can withstand tens or even hundreds of thousands of such cycles just fine, but it's still something I would avoid, just to be sure, if at all possible, by floating the cell with constant, regulated voltage instead.

--- End quote ---

Ok, well I'm designing this for a consumer grade product. So if this cycling can go on for tens of thousands of cycles it's more than enough actually.

But your other solution, this IC can't provide this, like most charging IC's can't as you said. But could it be a good design solution that in such a case I would switch off the whole charge IC and switch on a voltage regulator of about 7.4V (I use 2 cells in serie) to keep the batteries at that voltage? Then it's not cycling as you said and keeps it at constant 7.4V (which is 3.7V per cell) voltage. Or would this bring other problems?
paulca:

--- Quote from: Siwastaja on August 30, 2020, 12:58:16 pm ---When stored below about 50% SoC at room temperature or lower, aging is very slow (say, below 1%/year of capacity loss, or <5%/year ESR rise). On the other hand, stored between 80-100% SoC at elevated temperatures (say 40-50 degC), aging can be quite fast, say, 20% capacity loss per year or 50% ESR rise per year.

--- End quote ---

I used to take this as gospel as I read it hundreds of times and seen/read the links to Battery University where they had a little table. 

I wasn't until recently that I heard it challenged.  It's was AvE on YouTube who pointed out, there was no study, it was just a single table presented on Battery University and a few echo chamber sites picked it up, plus it being repeated constantly on forums.  Never any link or reference/source of this study or who did it.  No real data either.

So I searched and haven't found anything but Battery University and a few echo chambers.

The only real issue I can see with storing them fully charged is temperature.  In RC modelling were warned to not charge batteries in the field if it was cold unless we were certain they would be used immediately.  The reason is, the voltage will rise as temperature does.  So if you have 4.20V per cell at 5*C and take that battery home, setting your field bag down in a lovely 20*C room ... the voltage could rise 100mV or more and over volt the cell damaging it.

Do you have any references/sources with actual data testing life span against storage voltage and temperature.

On a separate, related point, my only evidence is that I have had two laptops which virtually never ran on battery, spent 99% of their lives plugged in and ... both batteries were found dead, unchargable, unusable when tested.  I put these down to the battery being cooked by the laptop which were run far too hot 24/7.
Siwastaja:

--- Quote from: paulca on September 03, 2020, 04:59:39 pm ---
--- Quote from: Siwastaja on August 30, 2020, 12:58:16 pm ---When stored below about 50% SoC at room temperature or lower, aging is very slow (say, below 1%/year of capacity loss, or <5%/year ESR rise). On the other hand, stored between 80-100% SoC at elevated temperatures (say 40-50 degC), aging can be quite fast, say, 20% capacity loss per year or 50% ESR rise per year.

--- End quote ---

I used to take this as gospel as I read it hundreds of times and seen/read the links to Battery University where they had a little table. 

I wasn't until recently that I heard it challenged.  It's was AvE on YouTube who pointed out, there was no study, it was just a single table presented on Battery University and a few echo chamber sites picked it up, plus it being repeated constantly on forums.  Never any link or reference/source of this study or who did it.  No real data either.

So I searched and haven't found anything but Battery University and a few echo chambers.

The only real issue I can see with storing them fully charged is temperature.  In RC modelling were warned to not charge batteries in the field if it was cold unless we were certain they would be used immediately.  The reason is, the voltage will rise as temperature does.  So if you have 4.20V per cell at 5*C and take that battery home, setting your field bag down in a lovely 20*C room ... the voltage could rise 100mV or more and over volt the cell damaging it.

Do you have any references/sources with actual data testing life span against storage voltage and temperature.

On a separate, related point, my only evidence is that I have had two laptops which virtually never ran on battery, spent 99% of their lives plugged in and ... both batteries were found dead, unchargable, unusable when tested.  I put these down to the battery being cooked by the laptop which were run far too hot 24/7.

--- End quote ---

Not interested in Battery University and other fake science sites. I have done my own extensive research, part of which was a 1.5-year measurement program of self-discharge and calendar fading, measured parameters were capacity and DC ESR, input parameters were different cell brands and products, state-of-charge during storage and temperature during storage. It was supposed to be put on a peer reviewed process and published but sadly never did because I left the university job far before the test time was finished. I have posted some data on this forum before, for example here:
https://www.eevblog.com/forum/projects/low-curent-pulse-charging-a-sla-battery/msg1868660/#msg1868660

As it stands now, it likely doesn't exceed the most stringent scientific requirements because the university support was cut off mid-way and the test finished for personal interest only, but what the heck, why not publish all the results, so here it goes, see the attachment. Feel free to share to others. Unfortunately, I lost interest in trying to maintain the heated cells heated once I had to repurpose the temperature controlled heatbed, and used whatever means and later estimated the average "warm" temperature. So take the "warm" dataset with a pinch of salt. The room temperature dataset (avg 22.5 degC, between 21 and 25 degC 99% of the time; air conditioning was available), and the "cold" dataset (actually monitored within +3..+5 degC) are useful, though.
paulca:
First thank you for that data.  It's at least an attempt at something.  There seems to be anomalies, maybe because it's not an easy test to do.  There appears to be false positive and false negative results for both arguments regarding storage voltage.  Although storage temperature seems more consistent to support not storing them hot.... like a mobile phone application spending 60% of it's time in your back pocket.  Even there mobile phone batterys have improved in that regard a lot with my current phone still lasting several days on a charge at 4 years old... running 24/7/365.  Much like my last phone it looks like it will become unusable not due to battery degrade, but due to the micro-usb socket failing.

So only looking at the top Samsungs.  The only one that showed any capacity fade after 1.5 years stored at 4.20V was the one stored at 35*C.  Was this battery charged at 35*C or charged at room temp and then stored at 35*C?  If it was charged at 15*C and then stored at 35*C then it's voltage would have risen above 4.20V and stayed there until it self discharged rapidly initially, but could have done the damage shown, no?

The first one stored at normal conditions at 4.20V seemed to gain capacity, though it's ESR rose(?).

I'm still not 100% convinced enough to discharge Lithium Ions I store for months as I may need them to be fully charged and it's honestly a pain to charge a handful to 4.2Vpc and then when I don't use them immediately discharge them and add a partial cycle to them.

One supporting bit of evidence for not storing them long term is that most products seem to come with some level of charge, but always tell you to fully charge before use.  However if you consider the environmental aspects of mass produced products being shipping around the world from China in container ships, the temperatures inside a container in the sun could easily get over 40*C, which even your data shows would harm a fully charged battery.

I feel if it was significantly important to not store them fully charged at the consumer end this storage charge advice would be in every copy and paste product manual.  Electric car owners would be advised not to keep their cars fully charged unless they are in use in the next few days. etc. etc.

I suppose one element of safety would be that a fully charged cell at 100% would carry a higher risk should it, for whatever reason, go into melt down than a 40% charged cell.
MosherIV:

--- Quote ---  I feel if it was significantly important to not store them fully charged at the consumer end this storage charge advice would be in every copy and paste product manual.
--- End quote ---

"Consumer" means sell as many as you can. So it is NOT in consumer electronics companies interrests to tell the customer how to prolong the life of the product.

It is well known by most who know something about LiIon batteries that it is not good to store then at full charge.
The reason is chemistry, at full charge where all the available lithium ions is in the kathode, there is a tendancy for the ions to stick to the kathode, ie lithium plating occurs. The process is irreversable.
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