Inside a LiPo (pics)

[Bigglesworth]

Hi Guys,
I had a 6S2P 4.4Ahr pack that finished an 80% flight with an imbalance of 200+ mV. After a cell balance to bring it back into line with the others I did a charge at 3amps. The cell imbalance was back.
So the pack was split up and the bad cell removed, It showed a small bulge near the bottom, on the side edge in the middle of what appeared to be a fingernail impression. The impression had opened up with the swelling.

Now to the interesting stuff, the other techs at work wanted to know what was inside a LiPo.
After we discharged the cell to 0 volts, out came the scalpel.

Here are the pics.

You can see the degradation of the plate where the swelling was in the third pic and the damage to the cell cover in the fourth pic. The degradation carried over to the adjacent plates as well but to a lessor degree.
Looks like the start to the destructive chain reaction that we have all seen on you tube.

There are two types of metal plates covered in the powder interleaved between the white membrane. The tabs of the like plates are spot welded together at the top.

enjoy.

-only one lipo was harmed in the creation of this thread-

[devious17]

Wow! That was an eye opener.

[atomicplatypus]

Thanks for sharing... that’s certainly educational! :)

[plasticbrain]

Nice work bigglesworth - an interesting insight into Li-po construction. You can see why an impact near the edge of a Li-po can be catastrophic... There is only very thin sheet of insulating membrane between each of the many metal electrode sheets.
Thanks for sharing,
Plasticbrain.