A123 26650 FIRE

[liveforphysics]

Encapsulation of cells into a protective polymer gives the cells a chance to survive in corrosive and humid use. Silicone polymers are one of the worst types to use for this, ureas and urathanes have proven themselves.

Sir, is this real? are U using solid resin to pack battery?
Or is flexible silicone resin flexible with thermal conductivity?

Remember cells expand/reduce with temperature and need air flow to breath..

bat resina2.jpeg

I’ve done a lot of intentional shorting of A123 26650s and haven’t been able to start a fire. Strangely the cells will greatly reduce current when shorted for a short time yet still show a decent voltage. It’s misleading and u can have a cell showing 3.6v but will barely put out current after being shorted for a bit of time.


My concern is this battery pack that i can’t balance and made with these cells. (Id planned to balance externally but for some reason now that the cells are built into a battery and potted and I drill through I can’t get a stable voltage from any of the groups and very weird. and I’ve now had two that have outgassed. I’ve done a lot of abusive testing on these cells including way overcharging and trying to charge cells that have outgassed and nothing dangerous has happened, making me feel safer, but I feel I’m pushing it now with this second out gassing bubble What u think?


It’s always said lifepo4 isn’t combustible even if u puncture it. That isn’t true and my friend drilled through one snd it ended in flames. It was a relatively minor fire that didn’t ignite the cells around but still. (he didn’t mean to drill it).

[john61ct]

Encapsulation of cells into a protective polymer

...

ureas and urethanes have proven themselves.

Please please link to products you think might be worth testing, ideally available in less than 44-gallon quantities...

Dielectric is assumed, but would any actually be thermally conductive rather than "too insulating"??

[Hummina Shadeeba]

WC-565 at bjbenterprises is what I’ve used and recommended

As far as if thermally conductive vs insulating I think would depend on the environment but if still air I think the resin will dissipate the heat better

[batteryGOLD]

Yes, Sir. U are correct.
But check tha structure diagram of cells

structure cell.png (76.24 KiB) Viewed 226 times

There is a disk vent. Means at some point cell could need to release inside pressure..
Even at natural many charge/discharge cycles some gas could be released by disk vent. Just saying..

LiPo cells do not have disk vent so maybe thats why those go fat!
What would happen to LiPo cells traped inside resin?

It’s a semi-hard polyurethane often used for potting cells. Cells don’t need air to breathe though and just some room to expand

[liveforphysics]

The cell's CID (current interrupt device) trips prior to the vent releasing. Notice the plastic gasket that isolates the lower aluminum area which receives the positive jellyroll aluminum foil weld joints. The vent is just stamped-in thin sections in the upper aluminum of the cells positive terminal assembly(steel bridge sits on top of this). The moment the vent does release, the cell is in a failed condition from the CID already being torn, but on top of this, the vent is not a 1-way passage, meaning it would permit humidity ingress to destroy the cell after the venting has spoiled the hermetic seal of the enclosure. I made you a quick scribble to show.

18650 vent CID small sized.JPG (159.13 KiB) Viewed 222 times

[Hummina Shadeeba]

I could still charge the cell even after it vented. Tempted to try again but it’s nasty. Vented at 6v and smoked at about 8v

I’m going to retire that battery but would like to know about these cells n other lifepo4 as relates to fire or smoking regardless.


The few A123 cells i saw vent it happened on the cell bottom.


The strangest thing for me was when I held cells in a short they would stop putting out current, and not get hot or throw sparks, but still show a high voltage. It seemed a voltage with no current.

There is a disk vent. Means at some point cell could need to release inside pressure..

I had two vent on me in that battery above.

[liveforphysics]

I could still charge the cell even after it vented. Tempted to try again but it’s nasty. Vented at 6v and smoked at about 8v

I’m going to retire that battery but would like to know about these cells n other lifepo4 as relates to fire or smoking regardless.


The few A123 cells i saw vent it happened on the cell bottom.


The strangest thing for me was when I held cells in a short they would stop putting out current, and not get hot or throw sparks, but still show a high voltage. It seemed a voltage with no current.

There is a disk vent. Means at some point cell could need to release inside pressure..

I had two vent on me in that battery above.

Sounds like you had a cell with no CID then my friend, high power cells sometimes don't have them, as the necked weld-nugget area that tears adds resistance. Sounds like in your example the CID disconnect mechanism malfunctioned.

If a CID and cell vent are designed to be capable of operating, the CID must first activate, as it functions by gas pressure accumulation to build up force adequate to tear the little weld nugget. If the CID didn't tear open circuit before the cell can pressure vessel was breached, then it couldn't be a pressure vessel to build the PSI inside the can needed to make the force on the CID diaphragm to tear the weld nugget, electrically isolating the cell.

Also notable, it leaves an ionic pathway to still show voltage on a DMM, but if you put any current on it the voltage falls to nothing.

[Hummina Shadeeba]

...

Please please link to products you think might be worth testing

Or no sorry this is what I used and was told commonly used for potting cells
https://bjbmaterials.com/wc-766-a-b/

[john61ct]

How bout you @liveforphysics ??

Please please link to products you think might be worth testing