# LiFePO4 fire.



## JRP3 (Mar 7, 2008)

You sure they were LiFePO4? Sounds more like Li Poly behavior. What brand were they?


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## McRat (Jul 10, 2012)

Hobby King's house brand. 

Yes, it surprised me. I've never had a lithium fire of any kind. Nor was I charging or discharging at a high rate. None were hot while cycling.

Inside they are pouch cells. They LOOK like the normal LiPo's from the outside, and they are marked at LiFePO4 on the outside along with nominal voltage.


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## McRat (Jul 10, 2012)

This looks right:

http://www.hobbyking.com/hobbyking/store/__10309__Turnigy_4500mAh_2S2P_30C_LiFePo4_Pack.html


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## McRat (Jul 10, 2012)

Only one pouch burned, and since it was the first time I was charging/discharging/balancing, I think the pouch had a defect.


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## frodus (Apr 12, 2008)

What charger?
Did you use a balance charger?
What were the cell-voltages before you started charging the pack?


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## lithiumlogic (Aug 24, 2011)

Are they very high C rate cells? As they're capable of greater short circuit currents when the separator is penetrated, maybe that's why they are able to burn.

I thought LiFePO4 chemistry wasn't supposed to go into thermal runaway till 400deg C? If charging them was making them that hot, surely you'd see the plastic envelope melting before things got that far


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## McRat (Jul 10, 2012)

It's a Thunder Sky advanced balancing charger set to LiFe so which goes CC then CV on charging, for discharge, it shuts off at the 2.5v under load. Charging, discharging, and storage all balance every second.

The batteries were 3.5-3.6v to start, right as they came from the MFR.

The rated discharge rate is 30-40c on 4.5ah rating.

I cycled to only ~3.5 Ah at 4.5a. Temps never exceed 26°C that I know of, none were hot to the touch, barely warm. I let them rest between cycles.

Then at the end I set to 3.6v for storage, all were balanced to within 0.02v. The ignition happened about 1 hr after storage mode, and was disconnected.

To anyone who thinks that there is no way for LiFe to ignite without abusing them, BS. My guess is mfr defect.


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## McRat (Jul 10, 2012)

Note: I'm not trashing LiFe. All my reading indicates it's far safer than other Li-Ion designs.

This is not the first "bad" battery I got from Hobby King. One Li-Ion had a short in it's balance wires, and killed the battery to 1.1v. But it did not ignite, it melted the plastic. Strangely, I force charged it after fixing the wires by using a desk voltage generator set at 4.2v and 100mA until it came up to 3.7v, then put it on a normal balance charger. It's still in use today, covered with electrical tape.

The 3 main things about this thread:

A) LiFe can ignite.
B) Hobby Batteries are cheap crap.
C) Hobby Batteries are cheap crap.


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## JRP3 (Mar 7, 2008)

McRat said:


> The batteries were 3.5-3.6v to start, right as they came from the MFR.


That might be the problem. LiFePO4 chemistry fully charged resting voltage is 3.40V. So either they were overcharged at the factory and damaged, or they aren't true LiFePO4


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## palmer_md (Jul 22, 2011)

JRP3 said:


> That might be the problem. LiFePO4 chemistry fully charged resting voltage is 3.40V. So either they were overcharged at the factory and damaged, or they aren't true LiFePO4


I was going to say the same thing.


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## McRat (Jul 10, 2012)

I should have taken better notes. 

The two survivors are fine. Overnight, both are sitting at 6.68v (3.34v) after their storage setting.

I don't think I will use them other than experiments though.

Both are bulged, as was the one that caught fire, which makes me think they were overcharged at some point, or defective in some way. 

I will be VERY reluctant from now on to use bulged lithium cells of any kind.


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## JRP3 (Mar 7, 2008)

Yes, a bulging cell is a damaged cell.

Read the comment section of the link you posted.


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## dougingraham (Jul 26, 2011)

lithiumlogic said:


> I thought LiFePO4 chemistry wasn't supposed to go into thermal runaway till 400deg C? If charging them was making them that hot, surely you'd see the plastic envelope melting before things got that far


It didn't go into thermal runaway or his photos would show nothing but ash. It looks like one cell developed an internal short and cooked itself.

And you can get LiFe to go into thermal runaway, it just takes a lot more to get it to go.


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## dougingraham (Jul 26, 2011)

McRat said:


> I should have taken better notes.
> 
> The two survivors are fine. Overnight, both are sitting at 6.68v (3.34v) after their storage setting.
> 
> ...


If they are bulged then they are damaged. One thing about puffed pouch cells is that the outside air pressure is not pressing everything inside together anymore. And when this happens you get hot spots that can cause the separator layer to melt and then you can have a conduction path between the plates and things go downhill fast.

I would discharge those cells to zero volts and then drop them off at a recycling place. While there isn't much chance of them popping off on their own they could.


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## lithiumlogic (Aug 24, 2011)

Jack Rickard had a seemingly unprovoked thermal event with the grey import A123 20AH pouch cells he was importing a year or so back.

At the time he was trying to find a way of making them into modules, started casting them into foam. Overnight, one of his modules split itself in half on the bench, it had been charged a few days previously. 

I suppose the risk factors are that 

a) the background of these cells was unkown, were they factor rejects?
b) very high C rate cells, in an internal short they can make a lot of heat very quickly
c) cast into foam, the cells are well insulated and have little ability to shed excess heat.



> you get hot spots that can cause the separator layer to melt and then you can have a conduction path between the plates and things go downhill fast


I've seen the graphs that show the rate of heat release for LFP cathode material vs temperature and it seems to indicate only a slow release of energy at 400C compared with a rapid release of energy at 200C for cobalt containing chemistries.

But once you get to 130C or so the separator melts and then imagine a fully charged, well insulated cell is not going to have a problem heating itself to 400C. Even if it doesn't get there, the flammable electrolyte may spray out under pressure and catch an electrical spark.

Although the cathode decomposition of a lithium cobalt cell occurs at 160-200C, there is a process that releases heat at a lower rate, down to much lower temperatures - breakdown of the SEI passivation layer?

A laptop cell, if REALLY well insulated, can go into thermal runaway by heating it to only 60C initially. Though it takes two days to get there.

I've certainly encountered laptop cells self heating before - getting "hot" during a charge , almost too hot to hold. I'd take it off charge and use a compressed air line to cool the outside of the cell down, but it would get hot again almost as soon as i stop blowing. Obviously the inside of the cell is still hot and will bring the outside up to temperature again but it took almost half an hour to get them to calm down, i can't believe something so small has that much thermal inertia, there must have been some kind of exothermic process.

Now the point is , are LFP cells also subject to this SEI passivation layer energy release thing, which could get them to separator melting temperature or not?


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## JRP3 (Mar 7, 2008)

Those cells Jack was using were most certainly rejects, and casting them in foam was a bad idea since it guaranteed that any hot spots would stay well insulated. Now he's casting prismatics in foam as well and selling them as batteries, another bad idea.


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## Karter2 (Nov 17, 2011)

JRP3 said:


> So either they were overcharged at the factory and damaged, or they aren't true LiFePO4


 Well some of those Chinese cells exaggerate and blatantly lie about their capacity and performance, "C" rate etc etc,...its not beyond belief that they might not actually be LiFepo4 ..as we know it !
Did you by chance get a charge/discharge plot from the packs ?


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## adder (Oct 16, 2012)

I have 2 of those it puffed into 2x the size (after about 8 months) and as of today its more then 3 years and they have lost more then 60% of their capacity but they never smoked.


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