So these batteries are just rolls of... electrodes? I don't quite remember chemistry class.
I'm surprised... I thought there were pixies inside.
I will mention there is a little trick that is common in Lithium Ion Secondary cell manufacturing, that may be used for Primaries...
What they do is they over-crimp the PTC into the cell, with extra pressure/force. This actually causes the PTC current threshold to rise a bit. I've heard that you can get an extra amp out of them this way, before they kick off. I've seen several papers that warn against doing this, for a variety of reasons.
If you look, in one of the photos, you will see an indentation on the PTC ring, from the crimp. You do not want to "overdent" the PTC, as it will defeat it's function.
The vent ring with vent liner is in the bottom of the top, then the PTC is put in, then the button top (all with necessary insulators/liners), then the whole assembly is crimped shut by the outer negative can portion.
The white porous membrane is typically a polyolefin (or other fluorinated polymer, like UHMWPE) membrane that is designed to melt (or maybe swell would be a better word) a bit and close up it's pores in a localized shorted area.
In Molicel's secondary cells, there is an additional very high temperature plastic membrane that adds an additional safety margin, were they said the single low temp membrane had been known to fail due to temperature. The low temp was still necessary, as in a localized spot, the temperature may not reach high enough to swell/melt a higher temp membrane.
One of the manufacturer's design guides mentioned that the typical vent is designed to rupture at 40 PSI.
Due to recent reports and pictures exploding 123 Lithium cell based flashlights, I took some more pictures for another thread, but I'm going to also put them here, so everything is also in one concise thread.
I decided to take some more pictures for folks of the button top and it's construction on the SureFire/Energizer and Duracell batteries:
I also ran another test, with a Duracell 123 that I cut open, and dropped in some water, at times it made more bubbles than you see in the picture, but that is about all that happened. It may be due to the limited rate at which the liquid water can actually enter into the tightly wrapped cell, which would be much different than a moisture filled cell that heats up...
Please folks, do
NOT EVER try any of the stuff I am showing you, I've seen some of these cells violently throw flames and hot molten material like a rocket engine. I have some special 1/2" thick plexiglass that I do all this stuff behind, forced ventilation in an open area, and thick welders gloves, and I still wear a full face chemical shield and sealed goggles, and a few other safety precautions.
Here is the internal construction of the Battery Station 123 cell, shipped to me on June 26th, 2006, manufacture dated as 02/06, and is brand spanking new, I've had it less than 2 days:
Overall cell:
Taking the wrapping off:
The top of the cell, with the black washer off:
Intact cell internals, can opened:
Seal end of cell, showing how the seal is made:
PTC on left, sitting on button, right side is vent assy with vent layer intact:
PTC closeup:
