2 month inspection of A123 cells

I wanted to give a update on my A123 module after a few months.  There is good news and bad news.  The bad news is that I have more bad cells, the good news is that there is a pattern to the failures.  I have 4 modules in my car, 3 are the original Mark 1 design and the 4th is the Mark II with the much stiffer endplates.  I did a pretty detailed inspection of all the cells.  The pattern to the failures is cell pressure, either too much in the case of module 2 or uneven pressure at the thin end plates for all of the early Mark I designs.

Module 1, Mark I, RevA: 1 cell had signs of electrolyte leakage and 1 other cell had a little spot that looks like mold.

This spot is the start of corrosion in the pouch.  The two cells were right next to the end plates.  I am upgrading it to Rev B.

Module 2, Mark I, RevA: Numerous cells had signs of electrolyte leakage.  Most of them were on the ends but some in the middle of the pack.  This pack was also problematic last time I inspected it.  My guess is that I over compressed the cells the first time I built it that caused undetectable damage. The second time I assembled it there was much less clamping force but I think the damage was already done.  I am putting this pack aside for now until I have a had a chance to evaluate it further.

Here you can see several cells failed from the pack.  In some the electrolyte is still trapped between the clear outer film and the silver inner layer.

Module 3, Mark I, RevA: 1 cell had signs of electrolyte leakage on one side.  This cell was locate right next to the negative end plates.  Failure looks like it was due to uneven pressure on the cell.  I am upgrading it to Rev B.

Module 4, Mark II, RevB:  I actually had a leaking cell for the first time on the Mark II module.  I didn't discover it until I checked each one separately.  The cause was quite apparent, user error.

When I had installed one of the cooling fins the sharp thin aluminum cut and tore the thin pouch material.  I cannot over emphasize how gentle you need to be with these pouch cells.  This is probably my biggest issue with using these cells. So I replaced the bad cell and also added electrical isolation using transparancies.  I only did half of the pack.  This way I will see the effect, if any.  I also upgraded it to Rev B too.

As with all my other posted I wanted to post what I have found with testing so far.  Hopefully it will save others some headaches if they decide to use the pouch cells, (or in some cases it might convince them it's too much work :-)  I expected using these cells to be a learning experience, but this has been more work expected.  I have spent more time and effort on the batteries then I have on the rest of the conversion but that is part of the fun of the project.  :)

The fallen cells