Lithium Battery question

[shadow460]

I tried modding a 2200 mAh Li-Ion battery for use in the PSP Slim with the slim battery door in place. In the process of opening the battery pack, I managed to slice through the silver cell casing. Sparks flew, and I was afraid I'd shorted something. The pack began to heat up slowly... uh-oh, thermal runaway... The battery never got uncomfortable to hold, so maybe what I thought was thermal runaway was really just heat being transferred from my hands to the battery.

 

Once I got the battery open, I noticed the cell casing folded in on itself. I fixed that and removed the material that was folded into the cell. The battery cooled. I worked with it for perhaps an hour, trimming the pads out of the case, exploring underneath the control board, trimming the electrical connector down, and looking for ways to make it fit.

 

It never did. The cell is just too big to fit into Slim without the big battery door. I put some electrical tape in between the layers of the cell casing that I'd cut. I think I cut through two layers, so I separated those two layers with tape to keep the outer layer from pushing into the cell. I reassembled the battery and tested it in my fat PSP, where it works just fine. The PSP-191 charger also recognizes and charges it ok. The cell's internals are not open to the outside, although the battery pack's black plastic case is. After reassembly, I put the thing in my fridge where I normally store Li-Ion cells.

 

Does the damaged cell casing pose a risk of thermal runaway? Should I get rid of the pack, or will it be safe to keep?

 

I know a lot about batteries, but I ain't jacking with Li-Ion cells anymore. I'll use 'em, but forget working on 'em.

 

EDIT: The battery is dead. A quick read at batteryuniversity.com revealed that what I cut into was the actually polymer electrolyte, not a cell casing of any kind. PSP batteries are lithium polymer, which uses a dry and sometimes a gel electrolyte. Battery university tells that the dry polymer is a non conductive plastic-like substance. That's exactly what I cut into.

I think what's happened to this battery is very similar to a Ni-Cd cell venting and releasing that white powder. That powder is also electrolyte. This means that the Stamina Pack will have less charge than normal since the electrolyte portion is damaged, and if there's gel inside, it will leak out like the Ni-Cd cell's powder does when the vents get stuck open.

Edited March 16, 2008 by shadow460

[Zerosquare]

In general, don't mess inside a Lithium-ion battery pack. They are so potentially dangerous if mishandled that manufacturers have to include special circuitry inside, to ensure that nothing catastropic happens if the pack is accidentally short-circuited or incorrectly recharged.

And even yet, from time to time there are product recalls, because of fires or explosions caused by a manufacturing defect.

[+remowilliams]

In general, don't mess inside a Lithium-ion battery pack.

That's very good advice. You risk fire/burns or explosion by screwing with them.

[shadow460]

Where I went was past the protection circuit. That's why I didn't want to risk anything with the Stamina Pack. I'm glad I chose the weakest of the three, but I seriously didn't expect to damage it like that.

It is no wonder there are so many posts about hard-modded Pandora batteries failing.

 

I'm sure I could have sealed the cut safely, but there was realy no need to take any more risks. I found out what I needed to know--at the cost of a pack that was already a little bit weak.

 

Now I'm going to go out and find some actual Slim batteries and a charger for them. That'll give me the spare power I want, just like I have with my fat PSP.

[Miqorz]

Sounds like we're in the exact same boat.

[supercat]

What's the best way of disposing of a battery pack that may be compromised? Set it outdoors away from anything flammable in a bucket of salt water to discharge it, or would that just make it more dangerous?

[Miqorz]

Throw it at Jehovah's Wittinesses. (sorry)

[shadow460]

What's the best way of disposing of a battery pack that may be compromised? Set it outdoors away from anything flammable in a bucket of salt water to discharge it, or would that just make it more dangerous?

 

Throw it at a Communist?

 

Throw it in the dumpster? Dumpsters are made of pretty solid metal, after all. I learned that by cracking my skull against one. Even if a fire did break out, the metal of the dumpster would probably contain it. Some types of acid don't like water too much, either.

In addition, "discharging" a lithium cells only brings it to the point where the cell voltage is 3.0 VDC. There's still a lot of electricity in there at that point. Short the cell contacts in any way, and you get thermal runaway.

 

Water and lithium don't mix well, although the polymer cells aren't as apt to explode.

 

Hmm, someone threw a cell phone battery into the pool where I worked last year. The battery bulged and refused to put out any voltage at all. They also threw in a Ni-MH pack, which lacked protection circuits of any kind. I expected the Ni-MH cell to be more dangerous, but both were obviously dead.

 

I'd say that the best way to defuse a thermal runaway is to hit the cell with carbon dioxide from a fire bottle. A continued blast should cool things down quite easily.

[supercat]

I'd say that the best way to defuse a thermal runaway is to hit the cell with carbon dioxide from a fire bottle. A continued blast should cool things down quite easily.

 

I would think the best way to handle a cell that's in thermal runaway is to simply ensure that there's nothing flammable nearby, and that there's adequate ventilation to clear out any noxious fumes. If one could force a damaged cell into thermal runaway someplace it could burn away without damaging anything, that would seem like it would probably be the safest way to neutralize it, but I don't know how best to do that.

[shadow460]

Makes sense. Maybe take it outside in the middle of the driveway and clip the contacts together?