A123 20Ah Pressure Thoughts--and bits for experiments.

[dnmun]

i do not use these pads. i just put them in compression and leave them alone between the end plates.

 

[megacycle]

I've been going through this document:

https://www.buya123products.com/uploads/vipcase/b24d4f5b63934c59d43e93b3bb4db60a.pdf

Forgive me if this was already covered in this thread, but I can't find it. The doc mentions:

Compliant Pads Between Cells
To Maintain proper cell support and account for expansion during the charge and discharge cycles, A123 uses a compliant pad between cells.

I'm wondering what makes for a "compliant pad" and what a DIY'er could use...

2 pages back aand stated in the document.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=52244&start=175#p1001593

 

[granolaboy]

The document states that they use aluminum plates, since they are excellent thermal conductors.

So you are saying I should find some of this poron stuff? I was thinking of using some aluminum flashing from home depot...

 

[megacycle]

The document states that they use aluminum plates, since they are excellent thermal conductors.

The only place I can find aluminum referenced in the document is in relation to extracting heat out, not compression.

So you are saying I should find some of this poron stuff? I was thinking of using some aluminum flashing from home depot...

I'm just passing on the information given in the document, should hope the professionals involved in producing the report, knew what they were doing.
I'd expect that the poron is a common enough material, they are using its trade name, I haven't had time to look into it much.
Expect any material with similar properties could be used, common sense.
Might want to alternate, Al, compression material, cell, as a tear in the cell wall can conduct through from cell foil inner bag.
Was considering a good anodised ( insulator), aluminum finish for the inner plates and compression just between the pack end plates and heavy busbar, but really only need this if your going to pull big 'C's' constantly to remove heat from the pack.

 

[whatever]

heres a pic of older a123 module, it shows black compliant pad, it might be different to what they use today, but it appears to be flexible/rubbery or similar material that takes shape of the cell its pressed against. Then there are rigid flat aluminium plates inbetween cells( plastic would do if low current applications)

 

[arkmundi]

flathill & liveforphysics posted an interesting article and provided some salient speculation regarding pressure and premature cell failure on the This is how A123 care about quality control thread. That thread is about visible foil wrinkles in purchased AMP20 cells and whether they're OK for use or not. The article:
Stress evolution and capacity fade in constrained lithium-ion pouch cells, by John Cannarella, Craig B. Arnold, Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA

• Highlights
• Stack stress is a dynamic quantity that evolves during electrochemical cycling.
• The initial applied stack pressure determines how stress evolves during cycling.
• Small stack stresses prevent layer delamination, benefiting long term performance.
• Higher stress causes higher rates of capacity fade through cycleable lithium loss.
• Stack stress leads to localized separator deformation and chemical degradation.

Certainly has me thinking again on best practices for battery pack construction using these cells. Part of a best practices approach would need to consider initial inspection, testing acceptance and/or rejection of cells, etc. Then how to go about making a pack with cell longevity in mind.

 

[h0tr0d]

Certainly has me thinking again on best practices for battery pack construction using these cells. Part of a best practices approach would need to consider initial inspection, testing acceptance and/or rejection of cells, etc. Then how to go about making a pack with cell longevity in mind.

The paper you presented says basically the same as the A123. Read from page 31 forward.
View attachment A123 20ah BOM!.pdf

 

[whatever]

cheapest material i've found that should suit for pads is double sided vinyl placemats, no good for high temperatures,
but for low temps should be good. They have very smooth surface and compressible.

 

[whatever]

another idea for a very cheap compressible material to go between cells is packing foam,
it wont be good for high temps but should work for low temp applications.

 

[Doctorbass]

Here is THE DOCUMENT you all have been waiting for.. It give you answers about A123 20Ah pack design engineering!

https://www.buya123products.com/uploads/vipcase/b24d4f5b63934c59d43e93b3bb4db60a.pdf

They mention what i always believed about compression of the cells: :wink:

see at page 32:

 

[whatever]

hey doc, it is good info on compression psi values, and compliant pads, that document surfaced some time back.......you missed it! back on jan 30th 2015 this page:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244&start=150
I discussed it a bit on this thread
https://endless-sphere.com/forums/viewtopic.php?f=14&t=69402&hilit=+compression