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Lithium Overcharge

5296 Views 35 Replies 11 Participants Last post by  JohnM, 
G
Got a good one for you all to answer. What is it that causes the Lithium battery to Swell when overcharged. What are the actual changes that cause this problem? I'm not looking for speculation here but actual factual information.

Pete :)
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rwaudio
gottdi said:
Got a good one for you all to answer. What is it that causes the Lithium battery to Swell when overcharged. What are the actual changes that cause this problem? I'm not looking for speculation here but actual factual information.

Pete :)
Click to expand...
Have you watched the video mentioned in the "lithium lecture" thread?
I think you can draw some facts from that.
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G
I have and I have but it is still not clear. My understanding is that the structure changes and it must be changing in such a way that it now takes up more volume but no longer accepts lithium.

Pete :)
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Jan
gottdi said:
I have and I have but it is still not clear. My understanding is that the structure changes and it must be changing in such a way that it now takes up more volume but no longer accepts lithium.

Pete :)
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What I understood is that the organic electrolyte changes at a certain temperature, and probably gives of a gas. An organic somewhat explosive gas. With LiCo a bit more explosive than LiFe. The fact the electrolyte changes into something that is not so effective in what it was designed for makes them go bad. And the gas makes them swell before the plug blows. So, never lett them swell. Unless the gas gan be absorbd again and the electrolyt changes back to its original chemistry after cooling down.
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G
I know they don't go back from swelling. The one swelled battery I took so I could take it apart is totally dead. One other I took to try to bring back from the dead has taken a charge but the swelling did not subside. All other batteries are fine. I only took the swelled ones for diagnosis. They did not cost me anything.
I don't think its gas. This is where I say, no speculation. I want to know for sure exactly what happens to cause the swelling.
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D
Not really a chemistry answer for you, but here's a data point. I torture tested some cylindrical cells until one vented (the cylindrical ones don't swell, they vent). It spit out electrolyte so hot it was a steam cloud, plus there was liquid electrolyte on the table. The cell was over 90 Celsius when that happened.

Apparently something gets hot enough to become gas. Sorry don't know if that's just boiling or a chemical change. Anyway, I found a spec for max allowed temperature of 80 Celsius, so now I limit the cells to 70 Celsius during tests, and no more venting events to date.
gottdi said:
Got a good one for you all to answer. What is it that causes the Lithium battery to Swell when overcharged. What are the actual changes that cause this problem? I'm not looking for speculation here but actual factual information.

Pete :)
Click to expand...
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dtbaker
the answers are in this video
http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387

very enlightening, but about 1:15 long!
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DIYguy
Hey Pete, did you get the Hi-Power pack that Motorguy got replaced? :)
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G
? Not sure what you are talking about?
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G
the answers are in this video
Click to expand...
Watched it already. I see no definitive answer. I am looking for definitive answers.
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DIYguy
gottdi said:
? Not sure what you are talking about?
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I was just wondering if your Hi_Power cells were from Motorguy. He had his pack replaced by them because some cells were damaged or something. Thought maybe u inherited them..since u mentioned a good deal, or free or something.....
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G
Got nothing from Motor Guy. The Freebees were dead or damaged batteries. My good ones were a good deal. Wish I could have gotten some nice 200AH CALBs but for now these will do.These will get me by while I save for better lithiums.

Pete :)
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DIYguy
I hear ya. I have CAlb 180's coming. U might want to check with Kevin...maybe u can pick up some more cells from him...
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dtbaker
towards the end, like in the last 15 minutes, he spent about two minutes answering a question on over-heat/overcharge. The overheat boils the electrolyte, becomes unstable, phase change, vents... bad news since the electrolyte is basically a flammable solvent carrying the Li back and forth between anode/cathode.

The other detail that I caught regarding overcharge is that it causes some of the loose Li to permanently plate on (cathode/anode), blocking effective transfer and Li movement, lower capacity, etc.
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G
Yes, I remember all that and that is what sparked the question. What exactly happens to cause swelling? I'd like to know on the molecular level what happens.
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G
maybe u can pick up some more cells from him...
Click to expand...
No need. I have plenty for two projects for now.
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dtbaker
gottdi said:
Yes, I remember all that and that is what sparked the question. What exactly happens to cause swelling? I'd like to know on the molecular level what happens.
Click to expand...

it sounded to me like the swelling of the plastic case prismatics was a combination of the heat softening the plastic, and the pre-venting vapor buildup as electrolyte starts to vaporize above 90-100 degC. He was talking about the metal can ones basically just rupturing along a seam, and the plastic case ones (TS/CALB) blowing out the designated weak spot in the top of the case.

I would extrapolate that once a cell swells, the bad thing is that it might allow the layers to not be in physical contact, which would disable Li transfer, which kills capacity. Sort of like a short across plates in a floodie. The conclusion for me is that if you are not pulling continuous high C amps enough to over-heat the electrolyte you are in good shape, and probably don't need to ever really worry about the endplate compression even.
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G
Again, I don't want speculation or extrapolations. I want exactly what it is and it looks like I need to hunt elsewhere for the answer.

Pete :)
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dtbaker
gottdi said:
Again, I don't want speculation or extrapolations. I want exactly what it is and it looks like I need to hunt elsewhere for the answer.

Pete :)
Click to expand...
try contacting that guy from the video... I'd say he could probably explain at an atomic level.
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G
I will be contacting them. I was hoping someone here was privy to that information. Hope they have the answer for me.

Pete :)
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