Damaged Cells

Dr. Dickie

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Sep 23, 2020
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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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I dont accept anything visible. Why gamble.
 

Bubba

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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
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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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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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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.
 

daromer

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You cant find much since manufactures does not allow dents into packs at all. They determine it to be an issue. Same as what happens when you extend discharge and cycles ALOT. Not much tested since manufactures also there have determined the degradation to be an issue earlier and therfore they should be discarded

If you want to gamble go ahead and use them but if you dont...

Just because you have 1 or 5 or 50 cells with small dents without issues that doesnt make it "safe" This is important to understand that it only takes 1 failure... Note that how 1 person uses the cells does not equate to how others do so we can safely say that dents arent good for the cells since they do impact the inside and they also impact the structure. To what degree is unknown but it does not make it safe.

Better safe then sorry!
 

OffGridInTheCity

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Its a delicate balance posting sometimes. As I said in my post, I agree with @daromer (and many others) that its not good to do. On the other hand, its the reality of my personal situation and just wanted to share for what its worth. For example, in addition to easily dented NCR18650As the blue modem cells https://secondlifestorage.com/index.php?threads/lg-lgdas31865-cell-specifications.1763/ from BatteryHookup had A LOT of small/large dents - some so subtle that you had to hold them to the light and look closely to see them.

So I know have many slightly dented cells - and I share that, not to advocate for using them but so you'll know this if I have trouble down the road :)
 

daromer

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Yeah agree. I have used Them too.. bit with that said i think we Always should add a disclaimer so not new People here read it and think it is 100% safe or standard procedure :)
 
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