How dangerous is soldering lithium ion phone battery, and how easy is messing up

Question

I plan on leading a workshop on how to create led devices(shoes, clothing, etc), and mostly plan on teaching how to do it with old electronics, like phone batteries. The point is trying to do it as cheap as possible, so getting something like a spot welder is out of the question.

I plan on attaching something like the picture below to the phone battery, and it looks like the only cheap way to do that is by soldering it.

Questions

From what I've looked up it looks like the battery can explode

1. is this explosion big enough to actually hurt someone?
2. How easy is it for the battery to explode for someone with not a whole lot of experience?
3. If getting seriously hurt probably won't happen, is ruining the battery a serious concern?
4. Is there a better option to connect the battery to a power source?

Answer 1

Have you looked at a phone battery? Your mention of spot welding doesn't match up with what a phone battery is. Spot welding is for batteries with hard cases and direct contacts or tabs instead of wire leads. Not to mention how you plan on charging these random scrap batteries to begin with.

I wouldn't solder lithium batteries as part of a workshop.

If they are phone batteries they will either have:

Leadless, direct contacts: It's too easy for beginners to overheat and damage the battery. Even if the battery doesn't catastrophically fail, you now have a damaged battery that may not look it and end up being hazardous in operation later on.

FPC (plastic film) connectors: Basically thin flexible plastic strips covered with tiny metal traces. It is too easy for beginners to short the closely spaced pins together while soldering or melt the plastic film (which could also result in shorting the battery). In any case, if that happens someone is going to have to grab the battery, toss it in a metal bucket, and make a dash for the door to toss it outside as it flames and smokes. Even if these two things were not issues, it would be fiddly to do and not suitable for beginners since they were never meant to be soldered to. Beginners have enough trouble soldering things that are made to be soldered, let alone something that was never meant to be soldered and would therefore require 4 hands.

Get batteries with real wire leads on them so you don't have to solder directly to the battery, or better yet pick a less volatile kind of battery. For an LED device, you do not need something as powerful (and volatile) as a lithium battery. AAAs or 9V would do fine and are standardized so you can get standardized wire connectors for them. I would prefer 9Vs for because with AAAs you would need more than one battery which means a bulky holder. Keystone Electronics

Answer 2

From what I've looked up it looks like the battery can explode

Yes, it could - probably not from soldering, but from shorting out or overcharging. That being said, most cellphone batteries have an internal protection circuit module (PCM) that prevents damage from short circuits, over-discharge or over-charge.

is this explosion big enough to actually hurt someone?

Yes, it could be. It could also set fire to other stuff and burn the building down.

How easy is it for the battery to explode for someone with not a whole lot of experience?

Quite easy. However the PCM (if present) significantly reduces that risk.

If getting seriously hurt probably won't happen, is ruining the battery a serious concern?

Again, the PCM should protect the battery from serious harm. Of course the soldering must be done properly, with the correct iron temperature, application time, flux etc. Battery contacts can be remarkably difficult to solder well (thorough cleaning and a flux designed for nickel often helps).

Is there a better option to connect the battery to a power source?

I suggest not using old phone batteries. Apart from the safety issues they may not be in good health, and really should be recycled. Cheap 2 or 3 cell AAA battery holders with a built in switch are readily available, and AAA dry cells can also be bought cheaply in bulk. Standard dry cells can't put out much current so accidental short circuits aren't so much of an issue, and they don't explode! Plus you don't need to charge them.