What are the dangers about soldering lithium cells ? - Page 1
Forum section: electronics / general

author: opablo
author_rank: Regular Contributor
timestamp: January 24, 2013, 07:16:44 pm
content: I need to connect a lithium cell (CR2016) to my compact/portable device prototype...And it can't survive even 1 ms without power so I'm thinking in soldering the cell to it instead of using a mechanical elastic/spring based connector.What about safety ? Is there a maximum soldering temperature that I need to obey ?Am I shortening the cell life by exposing it to soldering temperature for 2 seconds ?Is there any medical danger about this ? can it explode or release toxic fumes ?

author: SeanB
author_rank: Super Contributor
timestamp: January 24, 2013, 07:49:15 pm
content: Get the ones with solder pins on them, you get both horizontal and vertical versions. Then you just solder the pins. Soldering the cell is going to make it explode, as the stainless steel it is made from is not solderable, and the heat will melt the internal separators, they melt at 70C.If you use a cell holder just add a 100uF 10V tantalum or electrolytic, or larger value or voltage, direct across the cell to enable it to survive the transient, it will even store enough charge to enable you to change the cell when flat, provided the load is micropower enough.

author: marshallh
author_rank: Unknown
timestamp: January 24, 2013, 09:24:15 pm
content: Tabs are spot welded to batteries. The cells don't like high temperature.Get a cell with tabs already welded.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 24, 2013, 10:04:31 pm
content: Perhaps you should consider adding a capacitor so the device can survive. I think you might be able to spot weld the terminals on yourself with the proper power supply. DOes anyone care to elaborate?

author: opablo
author_rank: Regular Contributor
timestamp: January 25, 2013, 02:50:44 am
content: Thanks for the advises about adding a cap in the circuit and stop me from messing around with that.But I have to confess that -yes; it can be done-Wearing eye protection, not breading and using the maximum solder temperature (450C) I was able to solder wires to it first placing a tin ball on the battery and in a second stage soldering a tinned wire to it. In the first stage the solder touched the battery 2 times for 1/4 sec and I was blowing wind on the battery immediately after. And in the second stage the tin in the wire was pre-melted before touching the tin ball in the battery. And again... 1/4sec and immediately blowing on it. I cleaned oils from the surface prior to soldering and used 60/40 tin.I don't encourage u to do this but it's good to know that its possible.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 25, 2013, 04:50:54 am
content: I have countless LiPo and other related Lithium chemistry battery packs around. I keep them all in a closed fire safe. I charge them in a fiberglass fire proof bag. It's not really a great idea to solder the cells directly, but if your going to I would suggest hit the metal with some non conductive abrasive, clean, flux and hit it with a good enough size iron to not cool quickly and pre-tin. What you want to avoid at all costs is sitting idle with the iron on the cell. Correct preparation followed by very fast soldering and you'll be just fine. If your counting seconds..your taking way too long. Use more heat if needed to drastically reduce the solder time. Don't use more heat if your going to take the same amount of time.Another note...do not under and circumstances short the things out. I almost hate to give advice on bad practice.Jeff

author: codeboy2k
author_rank: Super Contributor
timestamp: January 26, 2013, 02:54:32 am
content: Quote from: marshallh on January 24, 2013, 09:24:15 pmI've soldered other battery chemistries before, but never a lipo cell. I usually sandpaper the nickel plating off the point where I want to solder, then clean it with IPA, flux it, then use a temperature between 800-850F on my iron. The wire is always pre-tinned and I put a ball of solder on the tip end. Then I just touch the wire to the battery terminal quickly for a split second and blow on it to cool it quickly so the solder hardens and I'm done.Does spot welding avoid heating because it's (A) small and (B) much higher temperatures?? how does it really work? I'm curious to know.Thanks!

author: RCMR
author_rank: Frequent Contributor
timestamp: January 26, 2013, 03:19:15 am
content: Never waste solder where a self-tapping screw will do!

author: Neilm
author_rank: Super Contributor
timestamp: January 26, 2013, 06:27:09 pm
content: Quote from: codeboy2k on January 26, 2013, 02:54:32 amBatteries are big so I'm surprised that just touching the iron to the battery gets a good connection. The big problem with Lithium batteries is that when they get hot you end up with an exothermic reaction- it start off hot and gets hotter leading to "an unintended thermal excursion". (Sounds much better than it explodes).Spot welding is used as the heat is present for only a very short time so the main mass of the battery does not heat up.Neil