The truth about A123 cylindric cells safety venting mechanis

[jumpjack]

I did dome research about the safety venting mechanism installed on cylindrical A123 nanophosphate cells, because I read several versions of this story in various forums, blogs and sites.

I ended up with this post on my blog, I hope it can be useful to somebody, although it looks like these cells are no more produced after A123 bankrupt and no-news from chinese Wanxiang company which bought a123 company.

"10" on the positive cap is the safety groove which makes the positive cap break upon cell failure, thus preventing explosion.

Instead, the hole in the negative cap is just a hole used to fill in the electrolyte:

Hence there is no need to use special tabs with holes: they were probably used by A123 itself, welding them to the cell while assembling them: in this case the hole in the tab had to remain accessible to allow filling up the cell; this probably allowed longer shelf life of the cells, as they were not activated until they were sent to the customer. Of coorse using tabs with hole for negative cap and normal tabs for positive would have added unneeded complexity to manufacturing process, so probably this is the reason why they used tabs with holes on both caps.

Tabs with holes:

Normal tabs:

 

[Hillhater]

Hence there is no need to use special tabs with holes: they were probably used by A123 itself, welding them to the cell while assembling them: in this case the hole in the tab had to remain accessible to allow filling up the cell; this probably allowed longer shelf life of the cells, as they were not activated until they were sent to the customer.

I don't see how the hole in the end of the tab has anything to do with "Filling " the cell.? .. ( do they actually "Fill" these cells after manufacture ?)
Isnt it simply there to aid soldering a connection ?

 

[jumpjack]

hSorry for my bad english, rather than a hole it is kind of a "crack" in the part of the tab welded to the cell; under the crack there is the cell filling hole.

 

[dnmun]

the electrolyte is added after the case is crimped and i would guess that the hole is left so the syringe can go inside the can to fill it up with the fluid. so there is no void volume left inside the cell i would guess. i wonder if they draw a vacuum on it first.