What happens to 18650 cell if soldered?

[SniperGaulois]

I want to visualize what happens to an 18650 cell if the caps are heated to 140 degrees C for 10-20 seconds.

As far as i know, the heat wouldn't penetrate more than 5% of the physical electrolytes, so 95 percent of the battery would be as new.

I don't know though because the heat perhaps goes deeper into the battery and 10% of it goes over 100 degrees and loses half it's cycle capacity.

It's discouraged and it for me it carries more mystery and scare factor than anything else, soldering is a mysterious taboo. How bad is a well soldered 18650, how much capacity is lost?

 

[Hillhater]

?......so 95 percent of the battery would be as new. .......?

...and if your bike chain breaks a link, 95% of it is still unbroken.....but it wont work !

Why dont you test a few cells, then "solder" them at 140C for a while, then retest .

 

[amberwolf]

Also, if you heat the insides past it's runaway-reaction temperature (see your specific cell spec sheets from manufacturer) it may well just burst into flame.

 

[SniperGaulois]

Yes i am interested in what the tests actually say regarding the performance afterwards... Batteries are amazing things, people can revive panasonics when they have been drained to 2.3 volts, and i saw a test for that, but i didn't tests for capacity after soldering.

You say a battery is the same as a chain? All the lithium inside the battery is simultaneously connected to the same connections, all i know is that it's a spiral rolled up to a continuous conductive foil. It's a chain reaction if there is a chemical change that propagates through the battery. If someone knows that, then they would have huge about lithium.

 

[redilast]

For cells with PTC devices, high temperatures cause the PTC to change phases cutting off the power temporarily. But when the cell cools down to room temperature the PTC could have its resistance increased for days, weeks, months or even permanently.

 

[Punx0r]

Assuming you don't immediately destroy the cell, the heat will cause decomposition of the electrolyte, creating contaminants/impurities. The effect of these on the battery over a long period of time is the problem.

 

[Pajda]

There is no significant life or performance problem with soldering terminals of any kind of electrochemical cell if you know how to do it = you will do it fast in a few seconds (up to 10s). For example almost all pouch cells pack are soldered. Electrolytic capacitors are generally soldered too.

The main reason why the 18650 cells are generally welded is because it is much more effective technology for mass production. Also the can (negative terminal) of common 18650 cell is made from aluminium which is not so ""solder-friendly" material. The cap on the positive terminal is also hard to solder with common techniques.

 

[Wheazel]

The general consensus is that soldering a 18650 cell is bad, as it damages the electrolyte.
However, if soldering is done under the best possible circumstances, like high energy iron and a few seconds of heat, then its very debatable how much damage there actually is.
I have asked this question in the past but never seen any comprehensive answers to it.
I have not bothered doing any tests myself either.

The only thing I know is that I have a pack from a few years back that's soldered and still works well.
Maybe all cells are equally "damaged" and maybe the bad effects were insignificant.

 

[Punx0r]

There is no significant life or performance problem with soldering terminals of any kind of electrochemical cell if you know how to do it

[citation needed]



Soldering the leads of a capacitor or the tabs of a pouch are not the same as soldering to the casing of a cylindrical cell...

The manufacturers say not to do it because the risk of damage ranges from insignificant to serious, with no way of knowing. Sure, you can get away with doing it to some degree or other. Just like you can usually get away with inflating your car tyres above the maximum rated pressure. It comes down to whether you want to start a battery build from reliable foundations (good quality cells, good layout, good connections, good packaging) based on sound principles, or whether other factors are more important i.e. lowest cost.

 

[Pajda]

Soldering the leads of a capacitor or the tabs of a pouch are not the same as soldering to the casing of a cylindrical cell...

It is all the same principle. The point is not to get critical amount of heat into the cell structure which will affect it.

When spot welding you are applying an extremely high temperature for a very short time - when soldering you are applying much lower temperature for a much longer time, but the overall amount of transfered heat could be the same. In the real world there is a big technology problem with control of the soldering process particulary if you are doing it with your hands.

When I started with life cycle tests of 18650 cells many years ago I have soldered tabs to few samples of Panasonic NCR18650B and after hundred cycles there were no significant difference against the samples from the same batch which were tested without soldering in the holder. Also in the past the soldered NiMh and NiCd packs were very common with no issues.

Maybe someone have other experiences but my opinion sounds that the main problem of soldering is a strong "discomfort" of this method closely associated with a high probability of damaging the cells against the spot welding.
So I can not generally recommend soldering too, but it works well even for 18650 if you have some experience with it

 

[Hillhater]

If your testing and analysis is at a similar level to you knowlege of materials of the 18650 can casings, then you may want to review your test methods again !
Soldering to cell casings is similar to playing Russian roulette.....some are Ok, some fail quickly, and some are little time bombs, burried in the pack just waiting to cause future problems.

 

[Pajda]

Indeed, I am just saying that the probability of significant damaging the cell by soldering is in a real world much lower than you are expecting. From the opposite perspective, did you see a study which declares that well made process of soldering cell terminals significantly affect their life? I have never problem with a soldered pack life, but I am not using soldering anymore because there is just no benefit against spot welding.

 

[flat tire]

Nothing much has happened to my pack and I have 95 cells all soldered. I made sure to not heat the cell for more than 5 seconds and cooled them immediately with air.

 

[Ianhill]

Ive soldered 18650 packs fine as long as you don't use a lot of solder and pre ruff the surface very little heat is needed at all some go wrong by blobing the cell with solder then introducing the wire rather than tin the wire and a dab of flux on the cell and touch them together 3 seconds of heat at the most very little solder used is the key and the cells never get warm at all to the touch, I used a busbar arangmeant so my cell wires are fuses and easy to tack on.
Some prismatic employ a first and last cell that can be soldered to then the rest of the tabs are aluminium some lipo packs use this to save money and time as they just spot weld them up.

 

[999zip999]

Big heavy tip. I use weller 80watt iron. Bigger better. Cleaned and well tinned. Heat for a while. Flux. Have a wet sponge ready to cool joint. Spot welding is best. Give it a test. You have test cells ?

 

[cwah]

I have soldered some cells of my battery pack and 1 string of cell failed within a year of use

 

[Allex]

Put cells into freezer, take a 150W iron, put a blob on the cell and a blob on the copper wire, join them together, takes 2 seconds in total when you heat the cell. The impact is minimal. The main goal here is not heat up the negative tab above 80-100C or there about. Because once the tab is hot it will heat up the negative electrode and then the rest. My 2yrs old packs works perfect still.

 

[Hillhater]

We all know soldering is possible...
...but that does not answer the OPs original question....

I want to visualize what happens to an 18650 cell if the caps are heated to 140 degrees C for 10-20 seconds.
.............How bad is a well soldered 18650, how much capacity is lost?

I have never actually done that temp/time, but i strongly suspect the cell will be toast !

 

[999zip999]

What just buy them pre spot welded in parallel strips from vendor. Solder 6p strips or ?

 

[Syonyk]

When spot welding you are applying an extremely high temperature for a very short time - when soldering you are applying much lower temperature for a much longer time, but the overall amount of transfered heat could be the same. In the real world there is a big technology problem with control of the soldering process particulary if you are doing it with your hands.

I can immediately touch the strip and cell with my bare finger after spot welding three blasts.

I challenge you to do that after soldering.