New cells swelling

Moonwalker

New Member
Joined
Sep 26, 2021
Messages
4
Hello everyone. I am new to LiFePO4 cells. My aim is to build a 12V house battery for my boat.
I bought 4 cells 200Ah from BLS (supposedly Grade A). The cells have black coating not Blue and they are unbranded but built quality and QR code looks ok.
On unpacking cells are a bit uneven with around 1mm difference from sides to center. Voltage was at 3.2V.
However after charging to 3.6V the cells swell up much more with around 5mm difference from sides to center. This looks a bit suspicious for me however a discharge at 25A did give 200Ah as specified.
I asked the supplier but he did not bother to answer at all.
What do you think?
 

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RCinFLA

Photon Sorcerer
Joined
Jun 21, 2020
Messages
1,165
I have a suspicion many of the new cells since about Jan 2021 are made with pre-lithiated anodes. It also roughly corresponds to the timing of change over to welded stud posts although they are functionally unrelated items.

Pre-lithiated anodes reduces the manufacturing cost by eliminating the manufacturing charge forming process and probably explains most of the 280AH to 300 AH capacity jump in same size/weight cell as pre-lithiated anode do not suffer the cathode lithium loss normal to regular manufacturing charge forming process.

The benefits to the manufacturers are too hard to resistance - lower manufacturing cost and higher cell AH selling price.

One side effect is some slight bloating on first few charging cycles. It is likely acceptable and should de-bloat over time.

Forgot to add the newer cells seem to have a bit higher impedance than older 280 AH cells. Instead of 0.15-0.18 milliohm they are typically 0.20-0.23 milliohms.
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Moonwalker

New Member
Joined
Sep 26, 2021
Messages
4
Use some mild compression and put them to work. Don't charge to 3.65 volts as 3.40-3.45 is plenty.
That's my next question. So far I am testing the cells separately. After discharge there is still some swelling but less. So should I compress them on full charge or discharged? And should I try to compress-inn the swelling or leave some space where the cells can swell?
 

RV10flyer

Solar Enthusiast
Joined
Mar 8, 2021
Messages
136
That's my next question. So far I am testing the cells separately. After discharge there is still some swelling but less. So should I compress them on full charge or discharged? And should I try to compress-inn the swelling or leave some space where the cells can swell?
My cell manufacture recommends compression while at the 25-30% SOC that I received them at.
 

curiouscarbon

Science Penguin
Joined
Jun 29, 2020
Messages
1,822
That's my next question. So far I am testing the cells separately. After discharge there is still some swelling but less. So should I compress them on full charge or discharged? And should I try to compress-inn the swelling or leave some space where the cells can swell?
From what I have gathered, the reduction in swelling may continue over further cycles. May not.

Unless we have a list of every electrolyte additive, which are often considered sauce, I think it’s not possible to definitively say what will happen.

Please observe safety precautions to protect self from battery, based on the degree of swelling, I would not be extremely alarmed, definitely alert.

I’m just an amateur and have seen only a few dozen examples of others projects.

If it starts looking like an opened accordion with your busbar, then we are talking real chance of hazmat time. That would be like 4mm+ per side swelling.

0.5mm cycle to cycle variance is specified in some data sheets at this size range, but it is apparently not uniform across the face of the aluminum cell wall
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
Oct 29, 2019
Messages
5,622
Location
Rural NE Ontario Canada
Ohh My, the rabbit warren of things here.
1) Ambient Temperatures will affect the swelling factor. Generally not very much - so this is a minor issue.
2) Charge & Discharge rate does affect internal cell temps due to the chemical interactions.
3) Expansion & Contraction is normal BUT it is not supposed to be excessive, the general allowance is 0.5mm to a max of 1.0mm (See Manfacturer Spec Sheet for particular cell type.

Compression VS Fixing. I will not do the 20 runs around the Mulberry Bush (which already has a terribly deep moat as a result. So in simple point form.
1) Ambient Temp should be between 20-25C (68-77F)
2) Cell SOC should be between 3.000-3.200 Volts per cell. NO Higher than 3.200 ! (THAT is the Nominal Mid-Point of the Voltage Curve (50% SOC).
3) They do NOT need to be squeezed ! A MAXIMUM is 12psi but 10psi (Pounds per Square Inch) is more than sufficient. That is hand-squeeze tight.

SPECIAL NOTES:
* NEVER EVER SQUEEZE OR FORCE CELLS ! Seams can pop as can pressure valves which means the cell is Junked !
NB: The Aluminium used for LFP cells is barely thicker than a soda pop can, keep that in mind !
** IF cells have expanded, discharge cells below 3.200 volts, even to 3.000, apply GENTLE pressure slowly and allow to sit for 2-4 hours (No Charging or discharging), then if still excessively bulged, you can squeeze again (GENTLY) and allow to sit a few more hours... Use a hard flat surface on the face (piece of plywood or similar) so that pressure is even across the faces of the cell. An Entire pack can be compressed in this fashion.
-> FYI / LESSON-LEARNED Dept: It is far simpler to Bind Cells into 4-Cell "Blocks/Modules" and then assemble your pack in 4,8,16 cell configurations as required. If for any reason you need to extract cells it's easier to pull out a 4-pc block and more manageable. Remember that 280AH Cells for example weigh 5kg/11lbs each, which can become unmanageable pretty quickly.

WARNING !
KISS explanation. Think of the contents in the cells like one long rectangular jelly roll with many many very thin layers (like flaky pastry thin). This makes putting pressure on them tricky as it has to be even across the surface. If one spot get's more pressure too fast it can weaken the material and spacing between the layers ultimately leading to a failure. Please do NOT "ManHandle" or force the cells, be gentle and polite.

Closing Note:
It is extremely RARE to see perfectly square/flush FLP Cells, it is just how they are made & assembled. There will always be a slight "wave" in the casings depending on temps & SOC etc... Even ABS Cased LFP like Winston or SinoPoly will "undulate" but less noticeable due to case design but it still occurs. They also recommend Binding/Fixing with MILD Compression.

THAT'S THE RUB: Folks are hung up on the term "Compression" leaping to the assumption that "force" is required, when only Mild Binding - Securing is what is being called for. This is all THANKS TO TRANSLATION SOFTWARE and how things are interpreted.

Hope it helps, Good Luck.
 
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