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diy solar

Swoll up like a Toad Frog

tinkerer

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The attached picture shows two 120 AH LiFePO4 cells that have been overcharged. Stupidly, I bypassed my controller, and connected a trickle charger directly, and then promptly forgot about it. I found them several days later swollen as shown in the picture with well over 7 volts (2 cells) . I have been using them since then, and they seem to be working fine, although I haven't done a load test on them. The sides are still firm, and when I squeeze them with my hand, I cannot compress them at all; I haven't tried any tools. They have not leaked, and there is no evidence that the seals on top have released any gas.

Please help me with your experience.

Q: Can I continue to use them? Is there any risk? I would like to do a load test and continue to use them.

Q: What is going on inside? Is the LiFePO4 cell expanded, or only the case?

Thanks.

Doug

I hesitate to mention this, but every time I post something on a forum nowadays, I get an answer from someone who has the most posts on the forum, but is not particularly knowledgable. Thankfully, I have been blessed with a good BS detector. 'Nuf said.
SwollenLiFePO4.jpg
 
Trash it. You are overthinking it. If you want to test it and use it, so be it.
 
I hesitate to mention this, but every time I post something on a forum nowadays, I get an answer from someone who has the most posts on the forum, but is not particularly knowledgable. Thankfully, I have been blessed with a good BS detector. 'Nuf said.
Was that statement intended to keep anyone from saying something you might find to be negative.
Those batteries are dead, I mean like the deadest I have every seen on the forum, excluding those that were actually on fire.
 
OK, there seems to be a consensus building here.

I suppose I want to know what is going on inside these cells, before I discharge them and perform surgery on them.

Robby, now that you mention it, most high-post responders are somewhat negative to my posts.

John, I am relying on my experience with other forums.
 
OK, there seems to be a consensus building here.

I suppose I want to know what is going on inside these cells, before I discharge them and perform surgery on them.

Robby, now that you mention it, most high-post responders are somewhat negative to my posts.

John, I am relying on my experience with other forums.
The electrolyte has been broken down to a gas.
 
If you want to tinker, sure, but I wouldn't rely on them for anything. And keep the tinkering away from anything too important in case they go poof and blow a bunch of crap everywhere. They won't go up in a huge orange fireball but it could still be messy.
 
Doesn't look like you blew out the overpressure ports.

The bloating is really just the metal outer can shell, although I have not dissected cells with such long and high voltage overcharge. Before I gave up on them and tear them apart, I would slightly put them under some weight to help accelerate gas leakage from plastic terminal grommets seals and allow metal case to deflate and bend back into shape. Don't force it too much and blow the vent ports out.

You can use the vent port outward bludging as an indicator of the internal pressure. Lightly push down with thumb on the port to gauge internal pressure.

Within a month or two they may deflate enough to get them roughly back in normal shape. You can then check their voltage, recharge if necessary, and load test them.

The real damage is how much electrolyte decomposition tar is now clogging up the electrode pores. This increases cell ionic transfer impedance increasing terminal voltage slump under load current. If voltage slump under load is not too bad, they may be still useable.

If you are impatient, you can drill a very small hole near the top, side edge of case and compress the gas out to get them back into shape. Then clean hole with alcohol and seal it with polyurethane glue, like Liquid Nails. Gas is mostly carbon dioxide with a little carbon monoxide so nothing really that toxic. Quantity of gas that leaks out of car exhaust pipe after parking in garage is much worse.
 
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If you want some research, there is a paper here called "Overcharge Cycling Effect on the Surface Layers and Crystalline Structure of LiFePO4".

From near the end of the paper:
overcharged with a current of 1 C to 6.0 V. This overcharge potential is high enough for destruction of the material itself. The same electrolyte decomposition process, together with partial destruction of LFP lattice and Fe migration to surface layer in form of FeF3 and Fe3O4, leads to deterioration in electrical conductivity and diffusion rate of lithium ions. A small amount of active material and constant temperature of the coin cells avoids thermal runaway and adverse processes, caused by cell heating. However, most decomposition products, attributed to high-temperature reactions (e.g., LiF and iron polyphosphates [34]) are found on the surface of the sample, charged to 6 V and, to a less extent, on the sample, charged to 5 V by low rate. It indicates that the potential of the cathode is the critical parameter for the failure of the overcharged cell, even if the good thermal management of the cell prevents it thermal runaway.

And from the conclusion section:
It was demonstrated that a short-time overcharge of up to 5.0 V by high currents is the least destructive and does not lead to an irreversible changes in the cathode material. However, an increase in the upper limit of the potential to 6.0 V or a decrease in the charge current to 0.25 C leads to, both, the formation of surface layers of electrolyte decomposition products, an increase in the polarization of the battery, and to irreversible slowdown of the lithiation kinetics of the active material.

So if you got to 7 volts, there is no hope for long term use of the cells.

Also from the abstract of the paper "Failure Investigation of LiFePO4 Cells under Overcharge Conditions", available to read on Research Gate:

A possible failure mechanism is proposed: during the overcharging process, metallic Fe oxidized first to Fe2+, then to Fe3+ cations; next, these Fe2+ and Fe3+ cations diffused to the anode side from the cathode side; and finally, these Fe3+ cations reduced first to Fe2+ cations, and then reduced further, back to metallic Fe. During overcharge/discharge cycling, Fe dendrites continued growing from both the anode and the cathode sides simultaneously, penetrating through the separator and forming an iron bridge between the anode and cathode. The iron bridge caused micro-shorting and eventually led to the failure of the cell.

Any time they are talking about the possibility of iron dendrites inside your lithium cell, you can be sure its not safe for normal use.
 
The attached picture shows two 120 AH LiFePO4 cells that have been overcharged. Stupidly, I bypassed my controller, and connected a trickle charger directly, and then promptly forgot about it. I found them several days later swollen as shown in the picture with well over 7 volts (2 cells) . I have been using them since then, and they seem to be working fine, although I haven't done a load test on them. The sides are still firm, and when I squeeze them with my hand, I cannot compress them at all; I haven't tried any tools. They have not leaked, and there is no evidence that the seals on top have released any gas.

Please help me with your experience.

Q: Can I continue to use them? Is there any risk? I would like to do a load test and continue to use them.

Q: What is going on inside? Is the LiFePO4 cell expanded, or only the case?

Thanks.

Doug

I hesitate to mention this, but every time I post something on a forum nowadays, I get an answer from someone who has the most posts on the forum, but is not particularly knowledgable. Thankfully, I have been blessed with a good BS detector. 'Nuf said.
View attachment 113654
I stripped a thread on one of my 302ah lifepo4 cells decided to drill it and re thread, drilled a tad too deep it didn't end well, toxic smoke and gasses, a lot of heat and £100 worth of battery ruined, but I'll never make that mistake again!!
 
I think just use them for another small project (eg. big usb powerbank, garden lights, etc) until they are completely useless, then recycle them. We all make mistakes and learn in our travels.
 
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