solder on positive side of battery?

[jmpaul320]

the only thread i could find on this was related to nimh batteries, but did refer to Li ions being particularly unsafe to do this with... with my limited knowledge i know that heat is bad for a battery and li-ions can potentially be an explosion waiting to happen if they are not respected and used with caution

so I have a few 26650s that are not button top and ive been using magnets on them for a short time, which i really dont like the idea of either ... accidental short and

is it possible, or even safe to create a small solder mound on the +ve side of the battery? im worried about heating it up too much with the iron. I have a basic cheap soldering iron that plugs into the wall (nothing fancy) and I would describe my soldering skill level as a beginner

any thoughts or recommendations? for now im sticking with the magnets until i can find a safe way to do this..:thinking:

 

[eebowler]

I've done it already on old 'removed from laptop' cells. Others will chime in here but, I think it's best to scrape off the surface layer of the little spot you're going to put the blob on. (from my experience, the solder sticks much faster when you remove the surface coating whatever it is.) Make sure your soldering iron is as hot as it gets so heating of the cell is minimal.

 

[jmpaul320]

i found another thread that said to put the cells in the freezer over night

does this really do anything? i mean were talking the diff between room temp and freezing is about 40 deg F and were talking about an iron thats heated to several hundred degrees

 

[czAtlantis]

I soldered on many cells and with proper tools it is easy with no harm to the battery.
First - don't use transformer soldering iron with simple copper wire as a tip...even it can have big power (100W) it has small heat capacity. Use soldering station with configurable temperature and large chisel tip!!! Mine is only 40W but because it has large thermal capacity it can deliver large amount of heat to the soldered surface.
Also you need proper flux!!!! Don't use (only) standard rosin - it will take long time and solder joint quality will be bad. I use solder flux for copper pipes etc (zinc chloride)- it is rough stuff and must be washed off because it is acidic but it works very good.
I don't think freezing the cell is good idea - soldering will be harder but cooling it down a little (fridge) can't hurt.
When I solder I first apply single drop of flux to the cell, preheat the solder iron with drop of solder on it to 300°C and quickly touch the battery for 1second max. I let the battery cool and then I continue with soldering any wire etc you need. I prefer doing this two-step because heating battery twice for 1second is better than once for 2seconds.
Soldering negative side is much harder because it is the cell itself. Positive side is just thin metal and it can be soldered easily because it won't sink the heat from solder so quickly like the negative side.
Scraping off the surface is I think optional - I never had any problems with the flux I use but if you have heavily corroded cell, do it.

 

[bshanahan14rulz]

I wouldn't condone soldering to a cell, since it can be hard to heat the connection without heating other parts of the cell.
1: keep localized heating away from the storage area of the cell and away from the PTC material that is directly below the + cap.
2: use flux.
3: use massive tip. More mass the tip has, the more heat it has available immediately.
the idea is to heat that metal cap so that solder will wet it, without heating the rest of the cell too much. I wouldn't try soldering to the - end, since that is thin metal with the actual cell electrodes just on the other side of it. No air gap, no PTC material, etc., in between.

As czAtlantis said, scraping the surface isn't necessary, and is probably what people do when they don't have flux.