When things go wrong... it can go really wrong!

Wolf

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Sep 25, 2018
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@daromer
Fortunately low voltage in a cell does not cause dentrits to grow it is the charging and cycling process esp with high current that does.
This is attributed to the evolution of Li metal morphology during cycling, which leads to dendrite growth and surface pitting. See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5126712/

My personal thoughts and beliefs:
Assuming that dendrites offer a resistance factor till they pierce the membrane and short the cell I believe that IR is affected negatively. I.e. Higher.
Additionally the surface area of the Anode is compromised resulting in poor performance hence capacity loss which we measure with our testers.
As with you I have no documentation for that belief.

Wolf
 

Dr. Dickie

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Sep 23, 2020
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Problem with low voltage is that the start to form dendrites. They are not visible but they are there and they cause fire in the end....
And what i know they are not visible to IR either. I cant find any datasheet that states that atleast.
Yeah, and that is what makes me concerned. But, I can't go back do it over. If I could I would.
Thanks
 

Dr. Dickie

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Joined
Sep 23, 2020
Messages
68
Fortunately low voltage in a cell does not cause dentrits to grow it is the charging and cycling process esp with high current that does.
This is attributed to the evolution of Li metal morphology during cycling, which leads to dendrite growth and surface pitting. See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5126712/

My personal thoughts and beliefs:
Assuming that dendrites offer a resistance factor till they pierce the membrane and short the cell I believe that IR is affected negatively. I.e. Higher.
Additionally the surface area of the Anode is compromised resulting in poor performance hence capacity loss which we measure with our testers.
As with you I have no documentation for that belief.

Wolf
Well, the good news is, I did all of my charging at 500 mAmps, so maybe I ameliorated some possible damage.
Thanks for the paper, that is good stuff.
 

floydR

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Aug 23, 2017
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792
What would be considered high current? max charge listed on datasheet? for LG M26 cells 2500 mA?
I know I have charged a few 39 mOhm cells that my Opus BT-C3400 drops the Amps down to below 100 mA building the ma slowly till approximately 2.8v.
They charge normally after that @ 1000mA and have a Ir of 34 mOhm.
1000mA is 2/5th the max rate
Later floyd
 

daromer

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Oct 8, 2016
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Interesting about the dendrites. I will see if i find the sheets showing low voltage and dendrites. Above only seem to look at those factors.
Could be i misread it.
Dendrites and charging during low temperatures is a big factor atleast.


Wolf: I guess dendrites can form without piercing until it reaches a certain point when it bursts? => no significant resistance change. Though just an idea i have not checked :)
 

Wolf

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Sep 25, 2018
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Dendrites and charging during low temperatures is a big factor atleast.
That is a subject that I have painfully come to grips with as the temperatures plummeted in the NE part of the US. My batteries are located in a shed that is not heated and lets say somewhat protected but certainly not tightly sealed and insulated. Hence I built my battery box with heating elements. Initially I had 200 Watts of heat which proved to be quite inadequate. I have doubled that to 400 Watts and it seems to "maintain" ~5°C.
I am incorporating new code into my ESP32 for an "emergency" 400W heating element to activate at 1°C if the present 400W still doesn't keep up.
I may also use the batrium expansion board relay for that. I will probably use a Server PS unit for that as they are rated at ~700W and should feed the 400W heating element quite nicely. Since most of the cold snaps happen at night and no charging takes place I am not to worried about cell temp till in the AM when and lately if the sun decides to grace my solar panels.

So what happens when a LI-ion cell gets charged at 0°C?

"When you charge a lithium ion cell in below freezing temperatures, most of the lithium ions fail to intercalate into the graphite anode. Instead, they plate the anode with metallic lithium, just like electroplating an anode coin with a cathode precious metal. So charging will electroplate the anode with lithium rather than, well, recharging it. Some of the ions to intercalate into the anode, and some of the atoms in the metal plating will intercalate later over 20+ hours if the cell is allowed to rest, but most will not. That is the source of the capacity reduction, increased internal resistance, and also the danger."
"This lithium plating of the anode isn't nice and smooth and even - it forms in dendrites, little sharp tendrils of lithium metal growing on the anode."
Ref: https://electronics.stackexchange.c...ge lithium ion,battery that is below freezing.
Additional Ref: https://www.sciencedaily.com/releases/2014/09/140903105638.htm
So you see my concern about charging my batteries at 0°C.
As you can see I am keeping my Battery box as warm as possible. Ignore the lack of temp sensors data on 2,3,4 as I have not installed them yet ran out of warm time.:p
Wolf

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Korishan

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I think this thread has gone off topic 🤔
 
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