Swoll up like a Toad Frog

[Swamplizard]

Had a pair do that when I was doing a top balance. They were the first LIFEPO4s I ever owned - purchased used from a local guy who had em in his "bugout" kit. When I tested them for capacity afterwards they were 25% of what they should have been. Need to drop em off somewhere - did I see above that Best Buy will take em?

 

[SparkyJJO]

Can't the BMS protect overcharging?

It was bypassed.

 

[chess-equality]

It was bypassed.

No wonder it's deadest. OP never do that again

 

[tinkerer]

When I said "well over 7 volts (2 cells)" that was the voltage of both cells. Each cell stayed well below 4 volts. Current would have been 0.5 A., or 2 Watts per cell. They never got hot. I messed with them today and they seem a bit softer than a month ago. I have been slowly discharging them.

John: Point well taken, Sorry, I should have thought thrice. As it turns out the well is still sweet and overflowing.

RCinFLA: With respect to an overcharge of 4 volts per cell rather than 7 volts, do your comments still hold? Is there any risk of creating a glowing mass of lithium (other than the usual ways)?

I am happy to leave them swollen. I made a new box for them yesterday.

hankcurt: Wow, Good information, I am sure. I am not sure these paragraphs pertain to my 4 V per cell overcharge.

Everyone, thanks for the information.

Doug

 

[chess-equality]

When I said "well over 7 volts (2 cells)" that was the voltage of both cells. Each cell stayed well below 4 volts. Current would have been 0.5 A., or 2 Watts per cell. They never got hot. I messed with them today and they seem a bit softer than a month ago. I have been slowly discharging them.

John: Point well taken, Sorry, I should have thought thrice. As it turns out the well is still sweet and overflowing.

RCinFLA: With respect to an overcharge of 4 volts per cell rather than 7 volts, do your comments still hold? Is there any risk of creating a glowing mass of lithium (other than the usual ways)?

I am happy to leave them swollen. I made a new box for them yesterday.

hankcurt: Wow, Good information, I am sure. I am not sure these paragraphs pertain to my 4 V per cell overcharge.

Everyone, thanks for the information.

Doug

Also use a proper busbar instead of that wire.

 

[tinkerer]

Also use a proper busbar instead of that wire.

As it turns out, the geometry of my cells has recently changed, and my "proper busbar" no longer fits. I thought that a 5" length of 14 AWG THHN would be fine for testing, since my highest current is 10 Amps.

Doug

 

[DThames]

....like a "dog tick" would be my choice term. It "dog ticked" on me would be a verbal use example of the term.

 

[LydMekk]

3.6 abs. max on these cells...
Live and learn! ^^ :D

 

[A.Justice]

My vote goes in the "those cells are trashed" column. They're still fun for experiments though. ?

 

[John Frum]

@tinkerer do you smell anything reminiscent of acetone?
LFP electrolyte is toxic and to me it smells like acetone.
Others have described it as a sweet smell.
To me it smells like nail salon that I pass on my way to the subway.

 

[tinkerer]

No,

do you smell anything reminiscent of acetone?
LFP electrolyte is toxic and to me it smells like acetone.
Others have described it as a sweet smell.
To me it smells like nail salon that I pass on my way to the subway.

No, there is no evidence of liquid or gas leakage. If I didn't see them, I would think they were working as if they were new.

 

[RCinFLA]

When you overcharge a lithium-ion cell and it bloats with gases, it means some of the electrolyte has been broken down to various detrimental chemical components. Most all lithium-ion cell chemistries use similar electrolyte solvents, mostly ethylene carbonate C3H4O3 (EC), and dimethyl carbonate C3H6O3 (DC). The lithium salt used, that is dissolved in electrolyte solvent, is lithium hexafluorophosphate (LiPF6) salt dissolved into the solvent to create Li+ and PF6- free floating ions.

Gases, mostly carbon dioxide, some carbon monoxide from solvent, and various small trace amounts other gases, including fluorine gas from electrolyte salts will do the metal case bloating.

The real damage is done by the solids of the electrolyte solvent decomposition. The solvent hydrocarbons create tars that gum up the electrode surfaces obstructing lithium-ion transfers.

This increases the impedance of cell resulting in more terminal voltage slump with moderate load current placed on cell. It also reduces the amount of available electrolyte in cell to carry the lithium-ion exchange transfer between cathode LFP (pos) and anode graphite (neg) electrode materials.

If you do dissect cell, when you unroll the cell laminate wrap, the graphite electrode material printed on copper foil should look solid, uniform dull black color. The surface of electrodes will have a brownish haze appearance when there is hydrocarbon tar present from electrolyte decomposition.

This is why a moderate load test, between 0.2 and 0.4 C(A) in amps and measuring the voltage slump between no-load rested voltage and voltage slump after one to three minutes of load test is a good test for cell quality.

If you severely overcharge for extended time, you can also destroy the cathode electrode. Under this condition, the least damage is cell is toast, the worst is cathode LPF goes into thermal runaway bursting cell and creating a lot of heat that sprays out the cell's guts.

 

[sirslayer]

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

 

[RCinFLA]

Usually, they can be used if electrolyte is not too fried, if only for lower load current applications. This is what you may get with used 'Alibaba' cells. Again, good reason to do a moderate load test on purchased cells. Series connected cell matching is another issue.

The only thing that usually expands is the metal can case due to gas pressure. Cell wrap is open at top to allow copper and aluminum foil terminals to escape the wrap, so most of the created gases escape into the can container area expanding it. The gas migration up through cell wrap laminations may also carry some electrolyte wetting from internal wrap and expel it into the metal case area. This further reduces available electrolyte within wrap.

The metal can case gas pressure will usually relieve by gas escaping plastic terminal grommets seals but it may take a couple of months to do so. If metal can is bent, it will keep that shape unless pushed back into shape.

A cell will increase in terminal voltage slump under moderate load current by 3x to 5x over its useful lifetime. Chart below shows what a new 280AH cells should have for current loaded voltage slump relative to unloaded rested open circuit voltage. Voltage reading needs to be taken directly on cell terminals.

 

[JoeHam]

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.

Google LiFePO4 dendrite formation.

It can lead to punctures.