LF280K 3.2V LiFePO4 cells "bursted"

[Craig1]

Hi everyone,

TLDR: some cells have burst/deformed whilst not being used, connected as a 48V battery, any insight would be appreciated! (Pictures attached)

In 2022 I bought 48x LF280K 3.2V prismatic LiFePO4 cells with the aim of building 3x 48V batteries. Only one of these batteries is being used regularly and the other 2 I've been cycling every 6 months and then storing at roughly 50-60% SoC. To cycle the currently unused cells, I'll have one set of 16 cells setup as a 16S1P 48V battery and swap it with the main battery I'm currently using with my SPF5000es, drain the battery to a low SoC by either lowering the charge amperage or disabling the solar then charge it back to 100% SoC. Repeat that for a few cycles and then do the same with the remaining 16 cells. One of the spare batteries has been sitting connected with a JK BMS with 2A active balancing (i could be wrong but i believe its the B2A24S20P model) whilst the other 16 spare cells sit in their boxes.
After cycling half of the spare cells (the ones that i'd left connected as a 48V battery), i was disconnecting them and noticed some damage to about 4 of the cells (as seen in the pictures), one of which was particularly worrying. All the cells stored in the boxes were fine and this is the first time I've noticed any damage to any of the cells over the past few years. The worst one had also left a indent in the wood it was stored on indicating it might of ruptured with quite a bit of force. (Yes i know i'm getting rid of the wood, even though it was planned to be temporary, silly idea..)

If anyone has any insight on why this happened i'd be very grateful! I've probably missed some important information out so please let me know and i'll try fill in the gaps as best as possible.

Thanks in advance!

 

[underdog5004]

That looks bad. Dendrites poking through the bottom? Corrosion of the outer aluminum shell? Gas generation, over pressure, burst and energetic release of gasses into wood? How did you know the unused cells were at 50% state of charge? Possible you were over charging them?

 

[42OhmsPA]

No insulators between the cells or on the bottom?

 

[LithiumSolar]

I suspect corrosion of some sort as well. I wonder if there was a dent or defect there that wasn't noticed as it was covered by the wrapper. Perhaps a pinhole leak?

 

[SparkyJJO]

How smooth is the wood you're using? I'm wondering if they abraded on a rough piece which eventually caused a failure.
I didn't even think of that when I was originally going to build a wood box for mine (now doing foam-lined metal).

 

[Skypower]

That looks like it’s from the inside out
All those little pucker points under the bottom seal, OH MY! They don’t look puffy, just violated from within. A bad corrosive cocktail in that batch?
Questions;
Real Eves?
Where from?
How did you find out or become aware?
Does it have an odor that you could compare it to?
Dang dude

 

[Sonne]

You haven’t mentioned what the voltage of the cells has been - have you been monitoring this in some way, or just assuming the cells are within their “happy range”? If you haven’t been keeping an eye on their voltage, to me it seems most likely some have become over discharged

 

[Supervstech]

Far more details needed…

We’re failed cells connected to a BMS? Connected when charging and discharging?

Pics of the build. Pics of the storage area.

Understanding why swapping cells around?

 

[bestconcreteblock]

This looks like some kind of environmental corrosion. Are these stored outside? I see daylight in the pics.

 

[upnorthandpersonal]

Is that pressure treated wood?

 

[Frugal Devonian]

Fake cells maybe?

 

[Skypower]

Looks like the fluid ate cellulose right out of the wood.

 

[Solar Guppy]

Never use wood for battery containers as it is a moisture sponge.

 

[740GLE]

Did you move actual cells around when trying to rotate them through? So you were disarming and reassembling bus bars and balance leads?

Or did you have 3 fully built batteries that you just rotated on and off?

The picture of the poky out bits from the cell outward from the bottom def seem like a cell manufacturing issue, but I can’t say too many issues like that have been reported.

 

[jorby]

Did you move actual cells around when trying to rotate them through? So you were disarming and reassembling bus bars and balance leads?

Or did you have 3 fully built batteries that you just rotated on and off?

The picture of the poky out bits from the cell outward from the bottom def seem like a cell manufacturing issue, but I can’t say too many issues like that have been reported.

That looks like crap stuck to the adhesive of the bottom insulator (or battery) before applying the insulator. If it is dendrites, that would be scary!

 

[740GLE]

That looks like crap stuck to the adhesive of the bottom insulator (or battery) before applying the insulator. If it is dendrites, that would be scary!

One way to find out!!!

Pull the bottom sticky insulator sheet off.

But you’re prob right, this is prob the most probable knowing some outfits love to rewrap cell.

 

[jorby]

I would worry that it might be something that could eventually poke a hole in the thin case. So yeah, I would be pealing that up and removing whatever it is.

 

[Frugal Devonian]

Environment too humid?