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18650 best soldering technique part2
#1
So following up on soldering and effects on cells, from this thread:
https://secondlifestorage.com/showthread.php?tid=9482
I wanted to observe & "over-do" soldering heat to see what might show physical signs of damage, so I destroyed a cell for science. 
It was water damaged & self discharged to 0.7V but otherwise physically OK, not corroded or punctured.
The cell was a Samsung INR18650-30Q from a power tool pack. Purple jacket, white top ring.
Ambient temp here at time of test: approx 16degC  

The soldering iron I used is this heavy duty one, the tip is approx 45mm x 18mm solid copper & measured at approx 330 degC with a non-contact temp meter. I think it's 80 or 100W (label is toast sorry)


For the positive end terminal, I soldered to & held the iron on it for least 15 secs.
The negative end was soldered to & held the iron on it for at least 20 secs.
(both timed with phone)   

At the positive end I found this:

Note the connecting strip. IMHO, this strip would reduce heat conduction from the pos terminal pretty well.
The white seal edge part around the CID/PTC terminal metal piece seemed to be very heat resistant (even tested with a gas torch, didn't soften, barely reacted)
The blue insulator ring (sorry bit out of focus) also seemed to be completely undamaged. It was easily melted if touched directly with the iron (gas torch made it shrivel up immediately).

I cut the cell length ways like so:

Then soldered the neg end per above, then let is cool for ~ a minute then peeled it open & found this:

Basically no damage, maybe some softening of the blue disc but not significant, still intact, pic looks worse due to me peeling open roughly.

But what about the white layer? To see what happens I soldered more:
So I unrolled some of the cell & found the copper sheet. I soldered to that with light pressure on a still tightly rolled part & it collapsed inwards noticeably (obviously not good):

Unrolling a bit more to see the result:

Pretty badly destroyed separating layer ....
So the separating layer is not good with soldering heat & will be easily damaged.
Even though easily damaged, I didn't notice any damage or changes at the edges, eg from neg case


I unrolled more & checked the pos strip area, no visible damage at all.



So given the above and the connecting strip at the neg end is much shorter so I decided to heat that more by directly soldering to the internal strip to see if heat from external soldering would/could do any harm.
Before internal soldering (note white insulation layer is 100% intact after previous external soldering for 20 secs):

After soldering directly to tip of internal strip (note insulation melted back):

This is the first obvious damage I've observed so far. But is even this a problem?
There are extra layers if the white & kapton tape (high temp) there.

And I had to solder to the internal strip directly only a few mm from that. So I don't believe it is a problem.

My observations & summary: 
- soldering for 20 secs with a large hot iron did no visible internal damage to either end of the cell
- at cell pos end, heat from soldering won't conduct to cell case much due to plastic seal.
- the pos end plastic seal seems tough & unlikely to be damaged.
- cell construction at pos end seems less likely to cause damage from soldering heat due to long connecting strip.
- the top & bottom (blue) insulator discs are susceptible to heat but seemed undamaged by soldering.
- the internal separator layer is easily damaged by soldering.
- cell neg end is more likely to suffer damage than pos end due to more direct contact of separator layer with cell casing 
- soldering at the center of the neg end (not at edges) would be better (more likely to heat separator layer at edges of casing)

Caveats: 
- I only tested on one cell
- other cells might be different
- there might be damage that's not visible, eg chemistry, subtle separator layer changes at neg end roll edge, etc
- air (from cutting cell open) might have influenced results (unlikely)
- my iron was ~330degC, hotter irons would increase damage probability
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#2
(08-09-2020, 07:06 AM)Redpacket Wrote: [...] Caveats:  there might be damage that's not visible, eg chemistry, subtle separator layer changes at neg end roll edge, etc [...]

Yes, that's a crucial point. For example, soldering can thermally damage the separator, e.g. it can fuse its pores, which can (locally) limit rate capability, possibly leading to Lithium plating then dendrites then internal shorts. It can also cause the electolyte to decompose, leading to various contaminant byproducts wreaking havoc.

To detect and analyze these and other microscopic changes requires high-end lab equipment, e.g. SEM (scanning electron microscopy) and XRD (X-ray diffraction), combined with solid knowledge of Li-ion electrochemistry in order to asses the impact of such damage.

That no damage appears visible to the naked eye does not imply that there is no damage.  In fact, generally, almost all damage and degradation is not visible by naked eye in a teardown as in the OP.

Again, recall that all respected Li-ion battery manufacturers explicitly warn not to solder directly to Li-ion cells.
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#3
The biggest concern is the inside that you dont see. You need a proper xray to be able to determine anything. Or an area where you can open it without pollution.
I have seen some d
Papers regarding this but only for normal testing and not soldering.
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#4
(08-09-2020, 04:49 PM)gauss163 Wrote:
(08-09-2020, 07:06 AM)Redpacket Wrote: [...] Caveats:  there might be damage that's not visible, eg chemistry, subtle separator layer changes at neg end roll edge, etc [...]

Yes, that's a crucial point. For example, soldering can thermally damage the separator, e.g. it can fuse its pores, which can (locally) limit rate capability, possibly leading to Lithium plating then dendrites then internal shorts. It can also cause the electolyte to decompose, leading to various contaminant byproducts wreaking havoc.

To detect and analyze these and other microscopic changes requires high-end lab equipment, e.g. SEM (scanning electron microscopy) and XRD (X-ray diffraction), combined with solid knowledge of Li-ion electrochemistry in order to asses the impact of such damage.

That no damage appears visible to the naked eye does not imply that there is no damage.  In fact, generally, almost all damage and degradation is not visible by naked eye in a teardown as in the OP.

Again, recall that all respected Li-ion battery manufacturers explicitly warn not to solder directly to Li-ion cells.

I understand totally why manufacturers say to use the lowest risk method - to protect their reputation & liability (especially in today's super litigious world).
While I agree none of us want bad outcomes, I don't agree we should be unreasonably scared about this.
We (you guys more than me!) have a large base of soldered cells and don't seem to be seeing incidents with cells.
This alone is a solid measure of actual issues.
Measurement of actual results is the best proof of anything.

There's a balance between theoretical, risk adverse manufacturers & the real world.
I agree spot welding is preferable but I also suggest soldering seems to be OK to.
Let's not forget that home DIY done spot welding is not nearly as well done as factory systems (we hope factory ones are done right).
Even re-using cells we don't know the history of is a risk.
The process of tearing of the old spot welded tabs is a risk - eg holes, pressure on seals, stretching of neg internal strap.
No process is perfect.
But as a group, we've developed techniques to test & looked for ways to do things that work & don't cause real world issues.
In my tests above I left a large hot iron attached for 20 seconds & there is no visible damage.
Areas likely to be damaged (neg end strap & neg end edge) have extra layers & materials present there.
Given the combination of info we have on soldering, I believe it's OK to use.
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#5
^^ It is certainly your prerogative to prefer cheaper higher risk methods. But please be aware that not everyone is willing to make the same risky choices, so they deserve to have access to all that is known so they can make their own decisions on such risks.

The thermographic images from the study that I posted here make it plain as day why soldering is much higher risk. That has nothing at all do with "corporate liability" and everything to do with basic scientific facts.
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#6
It's great we have multiple methods to connect cells but not everyone is going to use a spot welder, so we need to understand soldering properly too.
My interest is the question "how much of an actual risk is soldering" ie so we understand this method from as many angles as we can.

We respect your knowledge & scientific inputs, thanks for these, they're helpful & interesting.
Yes, soldering clearly gets cells hotter than other methods, not denying that or the science.
The numbers of cells soldered in the second life reader base is scientific data too (maybe not perfect, but data just the same).
The good thing about science is it's based on observations & measurement of actual as well as theory.

So my experiment was observing/measuring "can we show definite damage from soldering?"
So far, I haven't found anything definite & the cell appears undamaged from some deliberately heavy handed soldering.
I get it we might have to get Xrays, microscopes, etc out, but hey we've cleared the "oh look it obviously melted badly" stage.
Apparently only subtle possibilities are left.

Anything can be killed with too much caution....
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#7
(08-10-2020, 04:02 AM)Redpacket Wrote: [...] Anything can be killed with too much caution....

Alas, people have been killed by too little caution with Li-ion batteries.

And in some cases that was because they were never educated about the innate risks.

Education is not something that should be discouraged - esp. when it comes to matters of safety.
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#8
Mine are all soldered.  100w, light touch (2-3secs) once to stick some solder and second time (later) to melt the solder around the wire instead of sticking the solder to the cell - also 2-3secs.  

I remember watching a @Daromer youtube with 300w? *huge* soldering iron - a  few years ago now Smile   He was doing (what seemed like) <1sec per cell with quick touch, touch, touch.   Because of that I started with a 300w iron but it was too heavy (for me) to manipulate, the tip crumbled within a few hours, and I found that 100w was OK for me.  

Its interesting that some cell tops (+ side) solder quicker than others as in 1-2sec vs 2-3secs.   The NCR18650A tops take a solder dab with 1sec - e.g. quick dab - as they seem tinned?.  The grey cell tops take the longer couple of secs.   The bottoms are more similar in my experience - e.g. 2-3secs.    Note: I don't do any cleaning or scraping - just solder to the cells 'as is' with flux in the solder.   

I'm not planning to unsolder any of the 11,500 cells to date or change my technique - so eventually I'll be able to add a report on the long term affects of the 6 cell types I've used so far.   

First battery (14s122p) went online May 13, 2018.  Its now completed 752 charge/discharge cycles with 46.3% average DOD (within 3.5v -> 4.0v range).  No detectable degradation or heat or problems so far.   

If I live long enough,  I may be able to report more on the long term affects as the years go by Smile
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#9
(08-10-2020, 05:05 AM)gauss163 Wrote:
(08-10-2020, 04:02 AM)Redpacket Wrote: [...] Anything can be killed with too much caution....

Alas, people have been killed by too little caution with Li-ion batteries.

And in some cases that was because they were never educated about the innate risks.

Education is not something that should be discouraged - esp. when it comes to matters of safety.

Could you link any of that to anyone soldering cells?
Sure mobile phones, laptops & vape devices have all had issues (manufacturer original & untouched) but what about soldered cells?

All for education, hence the "solder for science experiment".
Running off solar, DIY & electronics fan :-)
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#10
(08-10-2020, 02:49 AM)gauss163 Wrote: ^^ It is certainly your prerogative to prefer cheaper higher risk methods. But please be aware that not everyone is willing to make the same risky choices, so they deserve to have access to all that is known so they can make their own decisions on such risks.

The thermographic images from the study that I posted here make it plain as day why soldering is much higher risk. That has nothing at all do with "corporate liability" and everything to do with basic scientific facts.

I'm having a hard time understanding why a video posted that shows the ends of cells getting hot but not damaged is more dangerous than the possibility of blowing holes in the metal casing with a spot welder. Basic scientific facts? What would those be?  I don't see what problems soldering heat is causing? I played the game of testing a group of cells multiple times for capacity, then soldering heavily on each end twice then multiple capacity tests again. I could find no cell degradation in any and all received way more heat than I normally use when soldering. Not plain as day to me anyway.....
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