LiFePO4 batteries explosion risk mitigation

[rlitman]

...How many Mac Books or Dells have you seen spontaniously combust?...

Well, back in 2000, I got a whole lot of replacement batteries from Dell due to a fire risk recall. Those were NiMH. But you make a good point. The reputable companies that put batteries in their equipment tend to use stuff that's pretty safe. The problem is that the market is awash in fly by night brands that are gone before a recall can happen, and they'll stuff whatever they can find from the lowest bidder in your Amazon package.

 

[JCrabtree4]

You had me up until that insanity. If that argument fails for propane or natural gas, then it fails for emissions of ANY flammable gas. And a venting cell releases just as much gas as the A2L refrigerants on the market that require flammable gas sensors that are such a big debate today.

I'm not suggesting that you should stick around a lithium battery that's undergoing thermal runaway. Whether it's emitting flames or not, a cell under thermal runaway is dangerous and you shouldn't be anywhere near it without significant PPE including SCBAs.

I am simply stating that LFP cells under thermal runaway do not reach the auto-ignition temperatures of the gasses they emit. Thus external ignition sources are required and you don't always have an external ignition source.

 

[JCrabtree4]

I think here we also need to differentiate between CELL thermal runaway and PACK thermal runaway. Everyone who says that thermal runaway isn't risky has only experienced the first. Anyone who's experienced the second knows your best option is to run away.

Thermal runaway is a cell-level phenomenon. While it can propagate from cell-to-cell through the pack, it just becomes a multi-cell thermal runaway. Safety standards like UL 2580 do not call out "pack thermal runaway" for a reason, rather they describe cell thermal runaway and propagation to adjacent cells.

Whether it's a single cell thermal runaway or a multi-cell thermal runaway, I wouldn't recommend living beings remain near it without significant PPE.

I never said that thermal runaway isn't risky. There are many risks, fire is only one possible risk.

 

[JCrabtree4]

I thought all plug-in EV packs were liquid cooled nowadays.

Nissan leafs used air cooled batteries until the 3rd generation was released this year. That's the only mass production EV that I'm aware of using air cooled propulsion batteries.

 

[rlitman]

...Thus external ignition sources are required and you don't always have an external ignition source.

We'll never see eye to eye on this one. Can you imagine a propane installer making this excuse? Here's an insurance perspective on it:

Tesla Megapack’s Sparker System: A Game-Changer in Battery Safety for Utility-Scale Energy Storage

As the world races toward a renewable energy future, utility-scale battery energy storage systems (BESS) like the Tesla Megapack are becoming critical for grid stability, storing excess solar and wind energy, and ensuring reliable power delivery. But with great power comes great responsibility—safet

www.linkedin.com

 

[theoldwizard1]

Okay, everyone like to see explosions ! Watch this video.

LFP Battery Explosion! Is it Possible??​

• He is using a fully charged LiFePO4 single cell. Fully charged is 3.65V
• He is over charging at 24 @ 30 A !!!!
• When the safety valve pops, it release hydrogen (H2), which is explosive
  • but H2 is lighter than air so it has to be contained
• An ignition source is required to ignite the H2 with the air

It does not explode (unlike Li ion which also vents O2), but the contained H2 does burn once it is ignited !

 

[Firebrick43]

Keeping them cool in daily operation and venting explosive gases are two separate processes. And an active fan needs to be independently powered. At the end of the day, the container probably needs to be outside with a lightly constructed lid.

Why do you need active cooling for them? People use them in boats, golf carts, RV's with no active cooling. If you are taking a charge out of them that builds excessive heat that passive cooling such as a spaced roof over the container and vents on the container can provide, it would be cheaper to get more batteries so you could reduce the draw rate.

 

[rlitman]

• When the safety valve pops, it release hydrogen (H2), which is explosive
  • but H2 is lighter than air so it has to be contained
• An ignition source is required to ignite the H2 with the air

The exact same arguments could be made about natural gas. The difference is that we have a long history of learning about natural gas failure modes. H2 still has an LEL and UEL, and the LEL of hydrogen is 4%. Natural gas is 5%. Propane has a shockingly low LEL at 2%, but the biggest risk from hydrogen is the range. The UEL is 77%, so unlike with most other ullage vapors where you can expect the UEL to prevent explosion, that's just not going to happen with hydrogen. With natural gas, the UEL is only 15%, so it doesn't take that much gas to go so rich that it's safe again.

To be fair there's less of a risk with venting cells, due to the hard limit on the volume a fixed amount of chemistry can produce. But lots of lithium cells are used in contained spaces.

Also "an ignition source" is wording I find painfully lacking in nuance. Gasoline takes around 0.8 milli-Joules to ignite. Natural gas has an ignition energy of 0.3mJ. Hydrogen is 0.02mJ! There's an order of magnitude difference here when it comes to finding an ignition source that people take way too lightly. We all know how easily natural gas finds ignition sources, yet nobody here seems to admit that hydrogen is over 10x more ignition sensitive.