Normal swelling of aluminium cased cells?

Turponieminen

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I am building a small 120Ah 12v battery, from those very common blue Chinese aluminium cased cells. 😆
During initial charging/top balancing to 3.65v I noticed cells swelling. They are 3-4mm thicker from middle compared from edge.
iam guessing this is normal.
I placed about 2 mm thick wooden stick sandwiched between double sided tape between cells so when i tied the cells together they are touching from the edges and leaving 0,5-1 mm gap in the middle for additional swelling.
is this better for cells or should the cells be clamped together more tightly to prevent swelling?
 

upnorthandpersonal

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This is normal. There are several threads on this board regarding the need to 'clamp' the cells together, in a fixture, etc. The EVE datasheet mentions to clamp them down. So does the Lishen one, and it is generally recommended to at least have them in a fixture.
 

DeeK

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I have been trying to find where EVE recommends clamping their cells and that doing so will increase their cycle life. I just downloaded the data sheet for the EVE 280 LFP and I don't see anything about clamping in there or differences in cycle life.
Here it is:

If someone can provide reference to where EVE states their cells should be clamped, I'd greatly appreciate their posting it, thanks!
 

DeeK

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@DeeK, that's an old version of the datasheet. The newest is on this site in resources. Search for 'fixture' - it's in section 6. Main Performance.
Thank you, I appreciate that. I chased it down and unless I got the wrong one, it was the same version I had. But, this time I did find the applicable section and their stated difference in life cycles depending on clamping. Very interesting.
I have been in discussions with Tony, the main dude for the Bestgo battery that ECPC sells. He had not heard of this and has no idea why they do it unless it's a Grade B battery. In those cases, he said humidity during assembly can cause swelling during charging but he sez swelling should not occur in top quality cells. I am not sure what to think...
 

Gazoo

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Thank you, I appreciate that. I chased it down and unless I got the wrong one, it was the same version I had. But, this time I did find the applicable section and their stated difference in life cycles depending on clamping. Very interesting.
I have been in discussions with Tony, the main dude for the Bestgo battery that ECPC sells. He had not heard of this and has no idea why they do it unless it's a Grade B battery. In those cases, he said humidity during assembly can cause swelling during charging but he sez swelling should not occur in top quality cells. I am not sure what to think...
I asked EVE about compression as follows:

Could you please explain the following quoted from your 280ah cell specification:

"At 25±2℃,the battery under 300kgf fixture : charging the cell with charge current 1.0C(A) and constant voltage 3.65V,0.05C cut off,rest for 30min,discharge to 2.5V cut off with the current of 1.0C(A),rest for 30min,and then start the next cycle,end with the capacity decrease to 80% of the initial capacity.The number of cycles is defined as the cycle life of the battery."

Why is a fixture required?

Is it to prevent expansion of the cells for longer cycle life?

If the cells are mounted in a fixture so they can not expand will that work?


And this was EVE's reply:

Hello,

Your understanding is right. During the charge & discharge process of battery, the cell will “breath” like people does- swell & shrink effect.
The function of fixture, we use the clamp, is to prevent the over-swelling effect, which is likely to cause electrolyte leak furthermore.
Thus the fixture will guarantee longer life.
Thank you & Best Regards


NOTE: When they refer to electrolyte leak they are referring to the innards of the cell. It is not external.

@ghostwriter66 called EVE to get more clarification. I would refer you to this post which is much more detailed than the reply I received from EVE.

There are many discussions regarding expansion of EVE cells. It's normal.
 

DeeK

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Is the swelling caused by outgassing during charging and then the gas is normally resorbed during discharge? If so, it kind of explains why slow charge/discharge are less likely to cause swelling. Is this only (or at least mostly) only a factor with the newer thin aluminum casings vs the older thicker poly casings? Is the issue that the expansion gradually allows the internals of the cell to migrate relative to each other, eventually disrupting the workings and shortening life span? If so, the constraints just ensure that original cell geometry and structure are maintained. I am wondering if the outer casings of the prebuilts, such as Battleborn and Bestgo accomplish the same purpose?
 

Gazoo

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Battleborn uses cylindrical cells...so it's not an issue.

The prismatic cells have a jelly roll in the container. The theory is the jelly roll expanding and contracting over time causes delamination of the roll. By keeping the jelly roll "tamed", cycle life is increased. Beyond that I don't know.

I can also tell you that my EVE's expand at low C rates. I am currently charging using a 12 amp charger and they do expand. But they also deflate. It's not much but it is visible.

As far as your other questions regarding poly incased cells, I don't know. It would be best to look at the manufacturer specs for other cells. I am only familiar with EVE cells and am beginning to become familiar with Lishens.
 

fafrd

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This is normal. There are several threads on this board regarding the need to 'clamp' the cells together, in a fixture, etc. The EVE datasheet mentions to clamp them down. So does the Lishen one, and it is generally recommended to at least have them in a fixture.
Does the EVE 120Ah datasheet have the same references to 300kgf that we all know and love from the 280Ah datasheet.

My only point is to not blindly what EVE is telling us about the advantages of clamping their (thick) 280Ah cells applies blindly and equally to their (thin) 120Ah cells...
 

DeeK

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This is an explanation about swelling I received from Tony, who heads up Bestgo batteries, thought others might find interesting:

The "expansion" due to breathing effect is allowed,. The "swollen" due to H2O caused is not allowed.

The "expansion" in breathing effect is due to lithium ion chemistry reaction, we allow such "breathing" in thickness, so in pack structure we use separators among cells, separators has center area empty to allow "breathing" of thickness. Here is a notice that we still use the pressing tools to press all cells together, then use fiber tapes to warp them and put them into a limited space to restrict the total size of whole pack, not let them grow much in thickness in the later time of cycle life.

But if a cell soon get much "swollen" by a short time usage, it is probably caused by inappropriate manufacturing of cells: The humidity is not controlled well and caused H2O joined the chemistry reaction to generate CO2 and H2O again during the cell usage time, soon caused cell became weak, or say those are defective cells.

--
In short, if a cell soon got big swollen, it is a low quality cell. But if a cell experienced thousands of cycles then get slightly "expansion" in thickness, it's acceptable. I am not so familiar with how much "expansion" of aluminum case cells should be, as we did not making them, but for our pouch cells, like 25Ah LiFePO4 cells, which has 4000 times cycle life, they normally have about 5% expansion in thickness at the end of cycle life, and we treat 10% expansion as maximum allowance value. Is that clear for you to distinguish "expansion" and "swollen" that I talked as above?

It is OK with us if you put my words on forums. So people will not be mislead if a low quality cell get swollen but still been treated as "breathing effect". Also, pouch cell is still quite different to aluminum case cells, so if an aluminum case cells have bigger "expansion", it is acceptable. Just beware of "soon got huge swollen" cells, as here is another factor of humidity should be well controlled in cell manufacturing process, it is a key point and hard point.
 

fafrd

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This is an explanation about swelling I received from Tony, who heads up Bestgo batteries, thought others might find interesting:

The "expansion" due to breathing effect is allowed,. The "swollen" due to H2O caused is not allowed.

The "expansion" in breathing effect is due to lithium ion chemistry reaction, we allow such "breathing" in thickness, so in pack structure we use separators among cells, separators has center area empty to allow "breathing" of thickness. Here is a notice that we still use the pressing tools to press all cells together, then use fiber tapes to warp them and put them into a limited space to restrict the total size of whole pack, not let them grow much in thickness in the later time of cycle life.

But if a cell soon get much "swollen" by a short time usage, it is probably caused by inappropriate manufacturing of cells: The humidity is not controlled well and caused H2O joined the chemistry reaction to generate CO2 and H2O again during the cell usage time, soon caused cell became weak, or say those are defective cells.

--
In short, if a cell soon got big swollen, it is a low quality cell. But if a cell experienced thousands of cycles then get slightly "expansion" in thickness, it's acceptable. I am not so familiar with how much "expansion" of aluminum case cells should be, as we did not making them, but for our pouch cells, like 25Ah LiFePO4 cells, which has 4000 times cycle life, they normally have about 5% expansion in thickness at the end of cycle life, and we treat 10% expansion as maximum allowance value. Is that clear for you to distinguish "expansion" and "swollen" that I talked as above?

It is OK with us if you put my words on forums. So people will not be mislead if a low quality cell get swollen but still been treated as "breathing effect". Also, pouch cell is still quite different to aluminum case cells, so if an aluminum case cells have bigger "expansion", it is acceptable. Just beware of "soon got huge swollen" cells, as here is another factor of humidity should be well controlled in cell manufacturing process, it is a key point and hard point.
yes, we are talking about normal ‘breathing’ and not bloating.

“so in pack structure we use separators among cells, separators has center area empty to allow "breathing" of thickness.”

This is for plastic-encased cells and is different than EVE’s guidelines for thick 280Ah cells which recommends use of a 300kgf clamping fixture to limit breathing in order to extend cycle life from 2500 cycles to 3500 cycles.

I do not know what EVE’s data sheet states as far as clamping fixture for thinner ~100Ah cells...
 

DeeK

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yes, we are talking about normal ‘breathing’ and not bloating.

“so in pack structure we use separators among cells, separators has center area empty to allow "breathing" of thickness.”

This is for plastic-encased cells and is different than EVE’s guidelines for thick 280Ah cells which recommends use of a 300kgf clamping fixture to limit breathing in order to extend cycle life from 2500 cycles to 3500 cycles.

I do not know what EVE’s data sheet states as far as clamping fixture for thinner ~100Ah cells...
yeah, i was just pointing out that if the cells are already encased, they're probably ok in terms of adequate constraint against swelling. i looked for the EVE 105Ah data sheet last night but couldn't find it. i emailed EVE for it so i'll post it if/when i hear from them.
 

HamptonHall

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While waiting to purchase my BMS, I put my 8 272ah Lishen from the group buy in parallel. To top balance--starting at 3.28 I slowly and finally got them up to 3.55. I, too, have the symptoms described above, with slightly "puffed" cells. I can't tell from the discussion how much "swelling" is too much, so would you look at my pictures? Thanks!
P1040025.JPGP1040026.JPG
 

HRTKD

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First, yes, your cells are swollen. Get some clamps on them, or something. Do this before you charge them any further. By allowing the cells to expand you may be putting stress on the cell terminals.

Second, your bus bars are incorrectly installed (slightly). They should not be installed from the bottom of one post to the top of the next. A bus bar should either be on the bottom of both posts or the top of both posts. The way you have them installed, the bus bars may not be making good contact with the cell terminals and other bus bars.
 

Gazoo

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While waiting to purchase my BMS, I put my 8 272ah Lishen from the group buy in parallel. To top balance--starting at 3.28 I slowly and finally got them up to 3.55. I, too, have the symptoms described above, with slightly "puffed" cells. I can't tell from the discussion how much "swelling" is too much, so would you look at my pictures? Thanks!
That's a lot of swelling. Did the cells come like that?
 

blutow

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Did that happen during charging? Based on how your bus bars look, it appears they were already bulging before you connected them (unless the busbars "slid" while charging). Where these cells from Basen?

I got a set of lishens a few weeks ago (group buy also) and they have zero bulge and sit flush with each other. They are actually a little concave if anything. I have not seen any evidence of significant expansion/bulging when charging, but I made a point to compress them before any charging and I discharge them to 50% before uncompressing
 

time2roll

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Seems like a lot of stress for the bus connectors to slide under the studs like that.
 

Gazoo

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While waiting to purchase my BMS, I put my 8 272ah Lishen from the group buy in parallel. To top balance--starting at 3.28 I slowly and finally got them up to 3.55. I, too, have the symptoms described above, with slightly "puffed" cells. I can't tell from the discussion how much "swelling" is too much, so would you look at my pictures? Thanks!
View attachment 42045View attachment 42046
I looked back and noticed you did not receive the cells in that condition.


I wonder what steps you took to parallel top balance? If you used a power supply and set the voltage of the power supply after connecting to the cells then you overcharged them. They look like they were overcharged. Did you verify the voltage at the terminals with a DMM? Did you verify the voltage of the power supply was correct? You need to bring the voltages of the cells down and see if they will deflate.
 

Gazoo

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Seems like a lot of stress for the bus connectors to slide under the studs like that.
They will slide. Mine have. I did not overcharge my cells. It happened when the cells naturally expanded and I have EVE cells.
 
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