spot-welding to 18650 cells - Page 1
Forum section: electronics / general

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 05, 2025, 05:38:44 pm
content: I have some new Samsung (unprotected) cells, an Aliexpress Lipo powered spot-welder (claims Max 650A, and measures fairly close) and what I assume is nickel 0.1mm ribbon ( it is magnetic) that came with the welder.It works just fine on the positive stud but useless on the negative - I'm assuming due to insufficient power, or incompatibility with in the metal, or both.There is no trace of adhesion on the battery, just a small dent.Anyone found a setup that works reliably ?

author: coppercone2
author_rank: Super Contributor
timestamp: October 05, 2025, 06:13:36 pm
content: you might need a laser to do that bond. The so called nail is its own assembly, usually welded to the little hat. Each part sourced at cheapest place.

author: voltsandjolts
author_rank: Unknown
timestamp: October 05, 2025, 06:14:18 pm
content: Quote from: coppercone2 on October 05, 2025, 06:13:36 pmEh, nope

author: coppercone2
author_rank: Super Contributor
timestamp: October 05, 2025, 06:15:05 pm
content: It will get dissimilar materials better then a spot welderand you can try dusting the positive with a fine grit rubber abrasive too. I had someone try to solder to nickel strip* (to solder to a already made battery pack) and in that place it only took when we hit it with a sanding stick. But you really should 'polish' it. I am not sure what happens if you spot weld to 'roughened' material, even if its clean. I assume its easier for the joint to fail.But we only were interested in a short term lab test, usually the work was disposed of as hazmat within a week or so.*most of the nickel strip we had soldered just fine. The really cheap stuff had issues. I think the issue might be a unspecified bath, where you get chromium (and other elements) in there too?The electrochemistry of nickel is interesting. You have watts nickel, sulfmate nickel and new high speed nickels. All have a different strain. Sulfmate nickel is soft. The hard nickels are shiny. The 'name of the game' seems to be rapid plating, with baths tailored for extreme current density for fast throughput. I never found information on how it ends up panning out for the jointery. Some of those nickel methods are not meant to be a top coat either, they assume its 'mid step' and you finish it off with other processes later. I assume bad things might happen if you get rid of those post steps.

author: Cyclotron
author_rank: Unknown
timestamp: October 05, 2025, 09:12:50 pm
content: Lots of posts about battery welders already hear on EEVBLOG Forums.https://www.eevblog.com/forum/reviews/suggestions-wanted-for-a-spot-welder-for-battery-tabbing/I liked the idea of at least assembling my own so I went with the Kweld.https://www.keenlab.de/index.php/product/kweld-complete-kit/I think he mentioned there were plans for something more commercialized once upon a time but I haven't looked recently.

author: thm_w
author_rank: Super Contributor
timestamp: October 06, 2025, 09:17:10 pm
content: New cells shouldn't need any sanding or prep, maybe a quick clean if they are dusty.Quote from: mikeselectricstuff on October 05, 2025, 05:38:44 pmInternal lipo cell based welders are garbage. That said, 650A should be fine for 0.1mm strip.What sort of pulse time?Whats the part number of the cell?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 06, 2025, 10:54:33 pm
content: Samsung INR18650-25Rhttps://cpc.farnell.com/samsung/inr18650-25r/lith-ion-e-cigarette-battery-3/dp/BT07511Despite a 16 page datasheet, no recommendations on welding to it...

author: sleemanj
author_rank: Super Contributor
timestamp: October 06, 2025, 11:11:28 pm
content: 0.1 really shouldn't be a problem even pure nickel, but you could try getting some plated steel strip instead.Maybe the lipo is bad, or underspecced

author: thm_w
author_rank: Super Contributor
timestamp: October 06, 2025, 11:13:28 pm
content: Yeah regular power tool cells, so nothing special about them that would mean welding problems.This guy is using a 2ms + 5ms dual pulse for 0.1mm, you can see it takes some skill and tweaking:

author: BradC
author_rank: Super Contributor
timestamp: October 07, 2025, 03:55:09 am
content: Sounds like the welder is a bit under-powered. Cutting a slot in the strip might be worth trying. It forces the current to take the long way round rather than through the strip and can help in a marginal scenario.Also as sleemanj suggested, nickel plated steel strip has a higher resistance and is easier to weld with less oomph available.

author: coppercone2
author_rank: Super Contributor
timestamp: October 08, 2025, 03:09:51 am
content: actually thermal mass makes sense, I forgot how the cells are built compared to non lithium. The positive is a disk that is compressed to mate it to other stuff (it has PTC in there). I wonder if the can body just might be thicker material that is thermally linked to the innards of the battery compared to the 'floating' disk positive. Even if it has the same thickness, it has a big air space under itBut 18650 do corrode, I have seen a 'sandy' orange/brown material form on old cells inside of things, usually on cells that are dead. But this corrosion is only on the positive side.and K-weld is damn powerful. IIRC I linked some rather thick steel with mine on the higher joule settings. I think it was 1/16th carbon steel. Way thicker then the 0.4mm advert lol. I think I was getting 1400 or 1600 amps

author: nctnico
author_rank: Super Contributor
timestamp: October 08, 2025, 11:55:12 am
content: Thermal mass shouldn't be an issue as the welds happen quickly. The current needs to travel through the material though so conductivity is important. If most of the energy runs across the nickel strip instead of through the welding area, you'll never get a good weld. IIRC battery pack manufacturers typically have slits cut in the nickel strips to force the current through the body of the battery.

author: coppercone2
author_rank: Super Contributor
timestamp: October 08, 2025, 08:53:27 pm
content: then why would it not work for the bottom but work for the top??Maybe they use a different composition of metal for the body instead of the top plate, since the top plate is much less formed?Easy enough experiment to do anyway, just weld two nickel strips together on top of a piece of stainless steel and try the same thing on a copper plate at the same settings. Or like something wet, since the electrolyte is wet.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 08, 2025, 10:32:41 pm
content: Quote from: coppercone2 on October 08, 2025, 08:53:27 pmThe metal surface does seem rather different between ends - it's probably a combination of the metal and the higher thermal mass

author: coppercone2
author_rank: Super Contributor
timestamp: October 09, 2025, 01:58:18 am
content: the body is severely stretched due to the dies. The top is just punched probobly from a sheet and then deburred.When you stretch the metal it makes it strange (take a look at DIY aluminum angle pieces for a extreme example, you can see actual tearing and weird grains if you do it fast without heat)At least that is one effect. IDK how visible it would be, but I assume that metal is sliding around in the crystal matrix some what