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pls explain me thermal runaway

oxyopes

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Aug 9, 2022
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Hi,
every resource I found tells me to use thermal insulation against thermal runaway (overheating) on my LiFePO4 batteries.

My definition of thermal runaway is that the battery starts to generate more heat than it can dissipate.

Thus thermal connection should be the solution, not thermal isolation. Using thermal isolation indeed accelerates the runaway, right?

Did I get it all wrong?

Thx!
 
I’m no pro in this field but my understanding is that one cell catches on fire and the heat from that fire catches the adjoining cells on fire till everything flammable is burning. Certain lithium chemistries produce noteworthy amounts of oxygen marking the event even more spectacular. On junkyard had a Tesla start on fire and the fire department got so tired of repeatedly returning to the same car that had rekindled it’s fire that they finally dug a huge hole filled it with water and dumped the car in it.
 
There might be spots where a heat shield should be used. No reason to insulate in a protected space at livable temperatures.

Thermal runaway is generally a battery that is pushed so hard the internal energy is igniting the materials creating more heat such that even when isolated for safety the battery continues to self ignite and burn using internal energy.
 
... I agree with you all on those points, but my question is still open :-/
 
Thermal runaway is not just a cell catching fire because e.g. the electrolyte vents and ignites. It's a cell heating up because the internal chemistry causes an uncontrollable self-heating process, which in turn releases more energy and increases temperature further. This can lead to fire, or explosion.

Now, this is mostly a problem with Nickel/Cobalt based chemistry such as NMC. LiFePO4 does not experience thermal runaway unless an external heat source is applied to get to the required temperatures where thermal runaway presents itself. Remember, it's not about the cell catching fire: it's about a self propagating effect where a cell heats up and causes a chemical reaction that keeps increasing the heat in a kind of feedback loop.
 
Remember, it's not about the cell catching fire: it's about a self propagating effect where a cell heats up and causes a chemical reaction that keeps increasing the heat in a kind of feedback loop.
And if I remember correctly the self propagation includes the release of oxygen from the process which is why they are hard to put out with traditional means of smothering them and depriving them of oxygen.
 

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The thermal blanket solutions are for NMC batteries nickle-maganese-cobalt & lithium these batteries are the ones that have thermal runaway. These are mostly small cylinderical cells such as the 16500 and 32500 as found in automobiles such as the tesla and many others ganged up in banks sometimes over 5000 cells, cooling cells gets to be an issue

Lithium-ferro-phosphate batteries do not exhibit thermal runaway

The danger with LFP batteries is the massive short circuit capability

Dropping a wrench on your automobile battery will make an arc flash and burn out and vaporize battery terminals and burn out parts of the wrench

Doing that on a big LFP battery will vaporize the wrench

I do not see any need for thermal insulation for LFP battery banks at worst they lock in the heat..
 
OK I believe the product linked is for other more volatile lithium chemistries. Not so much LFP. Specifically mentions cylindrical cells.

Although some have made an effort to separate the cells with a thin electrical insulator with heat resistance as a selection criteria.

Others have made an effort to put all in a big steel box. Probably unneeded. Others have contemplated a system to extinguish fire and heat such as flooding the steel box with water or a sand dump. All a bit extreme IMO.
 
thanks everybody!
Not against runaway, but against heating in general I was thinking about putting layers of aluminium between the batteries. These layers could connect to an outside radiator. When between batteries, I could electrically isolate them with a heat protection tape, just for safety.
But I do not know if it really brings any advantage for LiFePO4 batteries. Do you think it is useless work?
 
thanks everybody!
Not against runaway, but against heating in general I was thinking about putting layers of aluminium between the batteries. These layers could connect to an outside radiator. When between batteries, I could electrically isolate them with a heat protection tape, just for safety.
But I do not know if it really brings any advantage for LiFePO4 batteries. Do you think it is useless work?

Because of the efficiency of LiFePO4, your cells shouldn't warm up at all, especially with solar C rates. My BMS gets maybe somewhat warm at times, but my cells are always cold.
 
Do you think it is useless work?
Yes, useless for LiFePO4 batteries.

Your main risk is if an internal cell shorts out and causes a huge current rush from other batteries in your parallel array of batteries, you run the risk of a fire, most likely from melting cables.

Just make sure to properly fuse your individual batteries against huge over current if they are in parallel and you've done what you can. And make sure your connections are tight, etc.. yada yada.
 
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What better place to repaste this URL again, since it has Summary Tables showing the thermal runaway characteristics for each of the different lithium chemistries...

 
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