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Old Jul 24, 2015, 08:47 AM
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Pack Swelling - Intreresting Article

FWIW, article on why packs swell over time. (Does not apply to packs puffed from abuse.)
From EPEC, a Custom, build to print electronics business http://www.epectec.com/about/overview/ ,
Quote:
Swelling Pouch Cells

Swelling or bulging as a result of gas generation during charge and discharge is a concern. Battery manufacturers insist that these batteries do not generate excess gases that can lead to swelling. Nevertheless, excess swelling can occur and most is due to faulty manufacturing, and not misuse (Probably the cause of the swelling many of us have had with fairly new packs).
Some dealers have failures due to swelling of as much as three percent on certain batches. The pressure from swelling can crack a battery cover, and in some cases break the display and electronic circuit board. Manufacturers say that an inflated cell is safe. While this may be true, do not puncture a swollen cell in close proximity to heat or fire; the escaping gases can ignite. Figure 6 shows a swelled pouch cell.
Swelling can occur as part of gas generation. Battery manufacturers are at odds why this happens. A 5mm (0.2") battery in a hard shell can grow to 8mm (0.3"), more in a foil package.
To prevent swelling, the manufacturer adds excess film to create a “gas bag” outside the cell. During the first charge, gases escape into the gasbag, which is then cut off and the pack resealed as part of the finishing process. Expect some swelling on subsequent charges; 8 to 10 percent over 500 cycles is normal. Provision must be made in the battery compartment to allow for expansion. It is best not to stack pouch cells but to lay them flat side by side. Prevent sharp edges that could stress the pouch cell as they expand.



Swelling Pouch Cell Battery as a Result of Gas Generation During Charge and Discharge



Pouch casings are typically used for Lithium Polymer cells with solid electrolytes, providing a low cost "flexible" (sometimes in unintended ways) construction. The electrodes and the solid electrolyte are usually stacked in layers or laminations and enclosed in a foil envelope. The solid electrolyte permits safer, leak-proof cells. The foil construction allows very thin and light weight cell designs suitable for high power applications but because of the lack of rigidity of the casing the cells are prone to swelling as the cell temperature rises. Allowance must be made for the possibility of swelling when choosing cells to fit a particular cavity specified for the battery compartment. The cells are also vulnerable to external mechanical damage and battery pack designs should be designed to prevent such possibilities.
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Last edited by hoppy; Jul 26, 2015 at 08:09 AM.
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Old Jul 24, 2015, 11:57 AM
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Interesting indeed. I cannot imagine that swollen cell in the picture is normal. That looks like the kind of swollen cells that explode smartphones. Yes, I've seen an exploded iPhone in person. Owner claimed she had the phone in the carry-on luggage in the plane while it happened. It was not charging or turned on. There was no sign of fire. The swollen cell just cracked open the case.
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Old Jul 24, 2015, 12:39 PM
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I've seen a couple of notebook PC's where swollen cells cracked the housing. I wouldn't say that the swelling is "normal", but it's not particularly unusual either.
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Old Jul 25, 2015, 06:07 AM
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Yes I've seen cells swollen so badly on a few devices that the batteries were almost impossible to remove from the battery compartments. These devices were used only with the provided chargers and never discharged until shutoff. It certainly isn't normal, and is most likely a borderline defective battery IMO, though the manufacturers of course will never admit to that.
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Old Jul 25, 2015, 10:46 PM
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My daughters iPhone 5 has that problem, the battery is swelling the home key not working right .... I was going to order and replace, seems easy enough from the videos and I have experience - but I don't think I will try, others have had problems removing, and require some digging the cell out, which may puncture it. She has a 6 now!
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