Cell bloating

[mantonis]

I originally posted this under an old post regarding Ninthcit cells. That was possibly the wrong thread.
Here go...
I have just received 16 nos 280Ah Ninthcit cells, at least the cells have Ninthcit labels but the code on the cells refers to EVE.
I actually ordered grade A EVE cells from the supplier BLS Battery through AliExpress. The cells were courier delivered from their warehouse in Germany and they arrived within 10 days of shipment which is pretty quick for shipments from Germany to the Island of Ireland.
They were generally well packed but in a few boxes the terminals had partly penetrated through the cardboard box and punctured the plastic bag. Fortunately no terminals appear to be damaged.
I have measured the cell voltages and they are all within a range of 3.299-3.3020 volt..
There is no VISIBLE external damage and all the cells look clean. The QR codes are all in tact. All good so far. I still have to measure the impedances.

However some of the cells are obviously swollen but I have tried that quantify that by measuring the cells using vernier calipers with long jaws.
I have done that by determining the diameter of the cells across the width as I believe that swelling across the length is usually not an issue (correct me please if I am wrong!)
I first measured the width of the cells on both sides at the top of the cells (close to the terminals). I have found that at those locations the diameter is invariably smallest.
I then slid the vernier calipers to the bottom of the cells, again on both sides and noted the LARGEST dimension.
I put the results of this exercise in a spreadsheet and produced a delta between the smallest diameter and the largest one. I believe that represents the largest "bulge" in the cells.
Please note that I found quite a variation in the smallest width across the top of the cell (range 70.9 to 71.5mm), I assume that is the manufacturing tolerance.
The delta between the largest and smallest width was as follows:
One cell 3mm
One cell 2.8mm
One cell 2.4mm
One cell 2.2mm
One cell 2.1mm
One cell 2mm
Two cells 1.8mm
One cell 1.7mm
Two cells 1.2mm
One cell 1.1mm
Two cells 1mm
The other cells were under 1mm

Whilst bloated cells are obviously a concern I am not sure how much bloating is to be expected and how much would be unacceptable.
Can anybody quantify that? I have not been able to find any standards or specifications for LFP cells that bloating or swelling specifications/standards.
I am planning to put the cells in a pressure frame but I am concerned whether "flattening" the cells would cause internal damage.
As the cells are already charged to a 70% SOC I believe that they should not expand much more.

I would greatly appreciate any recommendations and advice.
Thanks
Mike

 

[sunshine_eggo]

Pictures would help.

The sheet metal casing is extremely thin and may appear distorted. The measurements you report to not indicate "bloat" "Bloating" is significant "inflation" of the casing.

Take two cells
place them together
get blocks of wood or books or something suitably large to cover the entire face of cells.
Sandwich the cells between those blocks
Firmly compress the cells together.

Can you force the cells flat? If so, you're good.

 

[Alkaline]

Ahh yes, another grade A aliexpress story. Let see how this one plays out, first thing is "Who is the reliable source" that told you, because we all know thats how these things start. ?

 

[houseofancients]

I originally posted this under an old post regarding Ninthcit cells. That was possibly the wrong thread.
Here go...
I have just received 16 nos 280Ah Ninthcit cells, at least the cells have Ninthcit labels but the code on the cells refers to EVE.
I actually ordered grade A EVE cells from the supplier BLS Battery through AliExpress. The cells were courier delivered from their warehouse in Germany and they arrived within 10 days of shipment which is pretty quick for shipments from Germany to the Island of Ireland.
They were generally well packed but in a few boxes the terminals had partly penetrated through the cardboard box and punctured the plastic bag. Fortunately no terminals appear to be damaged.
I have measured the cell voltages and they are all within a range of 3.299-3.3020 volt..
There is no VISIBLE external damage and all the cells look clean. The QR codes are all in tact. All good so far. I still have to measure the impedances.

However some of the cells are obviously swollen but I have tried that quantify that by measuring the cells using vernier calipers with long jaws.
I have done that by determining the diameter of the cells across the width as I believe that swelling across the length is usually not an issue (correct me please if I am wrong!)
I first measured the width of the cells on both sides at the top of the cells (close to the terminals). I have found that at those locations the diameter is invariably smallest.
I then slid the vernier calipers to the bottom of the cells, again on both sides and noted the LARGEST dimension.
I put the results of this exercise in a spreadsheet and produced a delta between the smallest diameter and the largest one. I believe that represents the largest "bulge" in the cells.
Please note that I found quite a variation in the smallest width across the top of the cell (range 70.9 to 71.5mm), I assume that is the manufacturing tolerance.
The delta between the largest and smallest width was as follows:
One cell 3mm
One cell 2.8mm
One cell 2.4mm
One cell 2.2mm
One cell 2.1mm
One cell 2mm
Two cells 1.8mm
One cell 1.7mm
Two cells 1.2mm
One cell 1.1mm
Two cells 1mm
The other cells were under 1mm

Whilst bloated cells are obviously a concern I am not sure how much bloating is to be expected and how much would be unacceptable.
Can anybody quantify that? I have not been able to find any standards or specifications for LFP cells that bloating or swelling specifications/standards.
I am planning to put the cells in a pressure frame but I am concerned whether "flattening" the cells would cause internal damage.
As the cells are already charged to a 70% SOC I believe that they should not expand much more.

I would greatly appreciate any recommendations and advice.
Thanks
Mike

and yet another one gets hit by cells from aliexpress..

bulging is irriversable, dont recompress them

 

[upnorthandpersonal]

Those couple of mm are not an issue. If they were looking like a balloon, that would be a different story. Even new cells aren't perfectly flat.

I would not put them in a 'pressure' frame - what I would do is make sure they're in a snug fixture, but don't compress with force.

As the cells are already charged to a 70% SOC

You can't say that for sure. Voltage is not an indication of state of charge for LiFePO4.

 

[sunshine_eggo]

Those couple of mm are not an issue. If they were looking like a balloon, that would be a different story. Even new cells aren't perfectly flat.

+1

I would not put them in a 'pressure' frame - what I would do is make sure they're in a snug fixture, but don't compress with force.

I hope it came across that my intent is to simply compress two cells together by hand to confirm any gaps can be close.

You can't say that for sure. Voltage is not an indication of state of charge for LiFePO4.

+1 I missed that bit. those cells are far more likely at ~30-50%

Pictures would help.

^ Reiterating...

 

[mantonis]

I have put them in a "mild" compression frame and used die springs to allow the cells to expand by a small additional amount as they are being charged. After assembly I found that the cells were actually at 50% SOC. They have now been charged to 100% without any obvious problems and have been discharged to 20% SOC.
Good so far!

 

[mantonis]

Those couple of mm are not an issue. If they were looking like a balloon, that would be a different story. Even new cells aren't perfectly flat.

I would not put them in a 'pressure' frame - what I would do is make sure they're in a snug fixture, but don't compress with force.



You can't say that for sure. Voltage is not an indication of state of charge for LiFePO4.

I found that the SOC was 50% but I still have to carry out a full discharge and charge cycle to confirm. I am a bit pre-occupied with other matters at present and will do so soon. In any case they are working out OK so far and the delta cell voltages remains small. I am using a SEPLOS BMS.