Damaged Cells

Dr. Dickie

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Joined
Sep 23, 2020
Messages
68
Part of processing cells is checking for damage. I have processed about 2K of cells so far, and a handful or so were seriously damaged. Just a glance and you could see the cell was crushed--into the bad bin.
A couple had a scratch, a serious scratch. The scratch was beyond just the PTFE sleeve--into the bad bin.
I have also come across a dozen or so cells that were like this:
Dent.jpg


Not a huge dent, but enough that if you get it in the light right, you can see it. To me, a dent is a dent--into the bad bin.
This dent almost seems like a manufacture dent, as there is no way it could be caused by being in or the taking apart of the pack. Maybe it was done by whomever made the packs, I don't know.
What level of dents do you accept?
Again, to me, dent is a dent, it is impacting the jelly roll inside in some way, no way for me.
 
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daromer

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Oct 8, 2016
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I dont accept anything visible. Why gamble.
 

Bubba

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May 9, 2018
Messages
261
I plan on binning the dented cells, but saving them for an outdoor project where my living isn't at risk :)
If there rust under the wrapper, I bin them for recycle. I found if rust from a bolt (external caused rust) hits the cell, then it causes the cell to rust a short time later.
Any smell from the cell (you learn the smell from ones with holes in them etc.... hard to describe the smell.) They get taped up and recycled ASAP.
Any white spots mostly seen on the negative terminal the cell gets taped and recycled ASAP as a possible leaker (happens a lot on the thin walled Panasonics).

Biggest thing I have learned is to tape the cell (I use box tape) so it is completely covered before binning them for Recycle. Scary moments o_O you learn quick!
 

anton_voltx

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Jan 13, 2021
Messages
8
Dents like this usually happen in shipping if the box was smashed on a side or corner. We have had it happen for a couple international boxes over the years. You are right not to use them... you should immediately send it to the recycling bin and find replacements. :)
 

OffGridInTheCity

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Joined
Dec 15, 2018
Messages
1,239
This site unequivocally and consistently advocates that all dented cells be discarded. This comment is just a personal one and in no way is advocating anyone follow suit - but rather just sharing info.

I personally use a <2mm rule. There have been other discussions about compression damage to 18650(s) and what it might mean. One snippet I read was that an 18650 'might' be able to withstand up to a 2mm lateral compression as a basic design characteristic and continue to function.

Here's a perfect example of a small compression dent that (presumably) occurred when I pried open a RING battery pack to get this out. Using a caliper, this dent is 1mm deep. These NCR18650A(s) have very thin canisters and easily compress as shown.
1610728112842.png


I have about 3,000 of these cells in 2.5 14s batteries and I would say that maybe 100-200 have small dents like this. Part of this, is that I did the <2mm rule accidently before even joining this site. Intuitively discarding major dents and accepting minor screw driver dings like this. And at this point, I'm just not inclined to dissemble 1,000(s) of cells looking for them.

So far (500 cycles @ 50% DOD) - no trouble - but I'm very interested in this subject AND especially what happens as cells age over the years. There's no harm in discarding these cells as the wise heads here on this site *strongly suggest*
 
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anton_voltx

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Jan 13, 2021
Messages
8
So far (500 cycles @ 50% DOD) - no trouble - but I'm very interested in this subject AND especially what happens as cells age over the years.
If that's a Panasonic then it has been impact tested without causing fire... but they don't cycle them after the impact either. The OEM guidelines are to do an appearance check before assembly into packs and if there's a dent then to do not use. If I had to guess what's going on it is that internally the dent is compressing / distorting some of the jelly-roll folds so there will be some imbalances making it harder for ions to shunt in some places and increasing degradation rate.
 
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