Is there interest in a group buy of A123 20ah prismatic pouch cells?

Top balanced at 3.44V

 

Balance them at 3.60, rested OCV. Remember that we have balancers to cope with small differences in cell behavior--not every behavioral anomaly indicates a real problem. Your small load is OK for capacity, but DCR tests ("ISR") should be run at 2C or greater, both for charge and discharge pulses of 10 or 20 seconds in duration. Your data is almost useless as is. That the sellers don't seem to recognize this should be of some concern.......

Are you familiar with Basic to Advanced Battery Information from Battery University

 

Thank you for the link. Your information is also authoritative, in my book.

Well, I agree my tests are not very conclusive. I used what I had at the time to prove out two suspect cells, that the vendor had already agreed to swap out, based solely on their serial numbers, cosmetic condition, and preliminary testing. He did not contest any of this, and did not demand to see any testing data. I take that as not such a bad sign. He did advise me at first to not worry about the bent cells, which worried me more, but has since offered to swap them out, too.

By the way, has anyone dealt with a bent cell?

As for top balance at 3.6V, your warning to not exceed 3.6 due to lithium plating had me choose something lower. I wanted to be absolutely sure I would not be damaging a cell I would be returning, and was not too concerned about getting a standardized AH number. I settled on a point where the 'knee' was pretty obvious, the voltage rising faster than 10mv/min (8A) at the top, falling at about 50mv/min (1A) at the bottom.

Keep in mind, at that point, I wasn't trying to prove anything to the vendor, we had already agreed two cells would be swapped, and I needed to find the best likely suspects from a batch that did not seem so differentiated as I had first thought.

But, now I have all these cells to choose from (none have been returned yet), should I set up a 40A load test?

 

For capacity/high self discharge testing, you want to be outside the knees, not between them. DCR/load testing should be performed between the knees, but with all cells balanced as best possible. Best practice is to balance at 100% and then expose all cells to the same exact routine during testing. Uniform temperature is also critical for getting valid results, especially with DCR. If you're doing this kind of testing in an environment with poor or no climate control, you're dealing with a major nuisance variable.

Read as much as you can from that Cadex site--it's a real trove of great info for batteries generally. Most of what you need here as far as I can tell is not necessarily specific to A123 cells.

 

Thank you! Sincerely.
But has anyone dealt with a bent cell?

 

About all I can tell you about that is I've flattened them back out and nothing catastrophic happened. I haven't had time to assess the long-term viability of a cell that's been exposed to this. Sorry I can't be more help on that one.

 

Hello wb9k,
I would like to have some discusions about LiFePO4 cells and about the information in the link that youout ito a previuos post...

I think it would be best to do this in a thread on that subject.

Thanks,
Dan Lander

 

You can discharge RFE Lifepo4 3.2vdc 20ah this low and still recover cell

 

Just a warning to all trying to buy A123 20Ah pouch cells from VICTPOWER, please take your time to read this:
The story of A123 20Ah cells from VICTPOWER
This company is not what it used to be… please google first and read review of your supplier, ask for samples!!! Then buy your A123!!!

 

Thanks for the info. They are obviously using A123 cells that had previously had their tabs cut off (probably rejects - tabless cells) and they managed to acquire them and spot welded new tabs on. They would need to expose the tab by removing insulation which sometimes leads to the cell becoming punctured. After the welding they probably used some sort of paint to insulate the weld.

Buyer beware.

There was a seller on Ebay who was selling tabless A123 20AH pouch cells but these cells are no longer listed so maybe he sold the remainder of his stock to Victpower.

Some of them looked like they were smacked around with a cricket bat maybe due to bad packaging of the delivery. I always ask the seller that they be delivered in their original packaging.

Just wandering. Did you get any warning from Victpower as to what condition the cells would be in before you bought them? How much did they cost? In this condition they were probably going real cheap.

 

Wow. John, I think these are the same cells you posted pics of previously, no?

Here's what happens. The Al foil pouch has a thin poly layer on its surface...inside and outside of the cell. A short between the cathode and pouch is not necessarily fatal, but when the poly layer gets punctured and creates a low impedance path to the anode (<5MOhms or so), Li begins to alloy with the Al pouch. This causes the Al to become brittle and fracture (decrepitation, technically different from corrosion). Those black spots around the perimeter of the cell are the signature of this phenomenon. Eventually the decrepitation breaks through the bag and the cell will leak electrolyte. If this happens after a cell is in a pack, it can lead to isolation faults between the failed cell and anything the creeping electrolyte touches.

Somebody has taken a bunch of scrapped cells that were rendered unusable, and tried to make them usable again. What you see here is the direct result of that. The seller is either ignorant, dishonest, or both. Good luck getting your money back...sorry about your misfortune.

 

What a misfortune, I'm sorry for you

 

That was a photo of what looked like a A123 20AH pouch cell with no marking and with two thin copper tabs which I assume they mistakenly sent me the wrong photo. All the cells I bought were delivered in their original packaging inside a wooden box. The original packaging makes the package a lot stronger structurally and are lees like to be bent during it's delivery. Which is a lot better than just packing them into one big cardboard box which is probably what happened to Elfi. None of the A123 cells I received were anything like the ones Elfi received. To begin with I just ordered one cell to start with to judge if they were genuine A123 20AH pouch cells and to me they seemed to be genuine.
A week ago I received an email from somebody who is now making a PHEV kit for his Gen3 Prius and 10 of the cells he received from Alibaba had welded tabs and when I emailed him back with a shortcut of Elfi's web page he replied that is exactly the cells he received. It is a definite sign that the Chinese are running low on stock of these A123 cells that they are going to the extreme of welding tabs.

 

This is a sign of very bad business practice; and to steer away from this.

 

I just found this listing on Aliexpress, it actually shows a photo of a A123 20AH pouch cell with welded tabs and paint over the weld. See second photo down.

Free shipping !A123 20ah prismatic pouch lifepo4 battery cell without logo on it-in Rechargeable Batteries from Electrical Equipment &amp; Supplies on Aliexpress.com

I guess if you ask for full size tabs you will need to specify that the tabs have not been welded on.

Below is a photo of a A123 20AH cell without any tabs. These reject cells have had their tabs cut off so they become useless. But a Chinese seller thought otherwise and sold them on Ebay. The seller removed insulation to expose some tab.



Below is a photo from the alibaba website showing how they had welded tabs to a tabless A123 20AH cell like the one above. They need to remove some insulation to expose the tab underneath to make a weld which results in a very good chance that the cell is punctured and will loose it's vacuum. If not resealed properly the electrolyte evaporates and it has a sweet addictive smell and you can smell it a mile away. Stay away from these cells.

 

Well people I have been around for some time, I had purchased 5-6 times from them earlier… I even asked for the pictures of the cells to be able to compare to cells I purchased earlier both from them and from OSN…
Pictures sent to me were exact the same, the thing is when you flip the cell from the back you do not see any difference; no weld to be seen; go back to the blog.
I have updated with some new pictures… here is one like that:




This is their way of recycling that we buyers are paying… this cell has damaged shell as well...

 

hey

does anyone want some A123 cells? that i have got jan 2012?

the bad ones are now gone because i have used them in a prius diy PLUGIN setup.

and used is a BIG word because i did not drive it a lot
i geuss in total its around a 1000 km on those cells

anyone intressed then send me a PM its for 70 cells.

 

FWD, What's up? You gave up the ghost on the Plug in Prius? I would be interested. I will PM you.