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Jan 16, 2010, 01:44 PM
Molon labe
Red Scholefield's Avatar
Thread OP

Why do LiPo packs swell?


THE QUESTION STILL GOES UNANSWERED

I have been using LiPo packs for nearly 4 years now and still canít seem to get a satisfactory answer from suppliers or manufacturers. What causes packs to swell? We know that misusing them will do it, too high discharge, discharging to a very low level, to fast a charge, but what about packs that have not been subjected to this.

I have several, from different manufacturers that are swollen significantly. These have always been charged on a balancing charger at well below the C/2 rate. It is interesting that these packs still have good power delivering capacity, just that they are swollen significantly. If anyone has had better luck than I have trying to get an explanation of the swelling under normal use, what the mechanism is, I hope they will share that information with the rest of us.
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Jan 16, 2010, 02:59 PM
Registered User
Carlyle Harper's Avatar
I've always thought it was the lithium reacting to something making some kind of gas that gets trapped inside the aluminum foil. As the gas accumulates it expands the foil.
Jan 16, 2010, 03:03 PM
I will be an angry old man!
marc1's Avatar
Quote:
Originally Posted by Red Scholefield
We know that misusing them will do it, too high discharge, discharging to a very low level, to fast a charge,

These have always been charged on a balancing charger at well below the C/2 rate. It is interesting that these packs still have good power delivering capacity, just that they are swollen significantly.
Charging at 2, 3, even 5C is not really an issue when the cells are properly matched. Charging slower than 1C is actually harder on the pack, as it will put more energy back into it.

Do you ever charge and then let the pack sit for 3-4 days?

The Lipo cell chemistry is somewhat unstable and degrades over time. This process is accelerated when the cell is left unused in a fully charged state. Handling, such as dents, bends, punctures will also affect the cell's stability.
Jan 16, 2010, 03:03 PM
Molon labe
Red Scholefield's Avatar
Thread OP
Quote:
Originally Posted by Carlyle Harper
I've always thought it was the lithium reacting to something making some kind of gas that gets trapped inside the aluminum foil. As the gas accumulates it expands the foil.
True, some kind of a gas is being generated. I heard it is the solvents used in the process. But what causes this on some packs and not on others? What impact does it have on the performance - I haven't noticed much in that regard. Swollen packs still giving good performance after 3 years use.
Jan 16, 2010, 03:06 PM
Southern Pride
everydayflyer's Avatar
Where is hoppy when you need him? He has all the links to obsure White Papers.

Puffing caused by over heating as during high rate discharges will go down in most cases. Puffing caused by over charging does not normaly go down. Puffing caused by discharging to zero volts is also permanate. These are my observations.

Charles
Jan 16, 2010, 03:07 PM
Molon labe
Red Scholefield's Avatar
Thread OP
Quote:
Originally Posted by marc1
Charging at 2, 3, even 5C is not really an issue. Charging slower than 1C is actually harder on the pack, as it will put more energy back into it.

Do you ever charge and then let the pack sit for 3-4 days?

I have not observed this at lower rates. Input seems to be the same to the 4.2 volts cut off (Cell Pro 4S) regardless of the charge rate. I always charge the packs after flying and they may set for several days until the next flying session.
Jan 16, 2010, 04:12 PM
Space Coast USA
hoppy's Avatar
Quote:
Originally Posted by everydayflyer
Where is hoppy when you need him? He has all the links to obsure White Papers.

Charles
TankU, I needed a smile today.

I have seen a partial answer to Red's question in my wanderings.... from an obscure web page showing the gases formed under different situations.
http://criepi.denken.or.jp/en/e_publ.../00seika41.pdf

Under "Normal Operating Region", see the last item, see Generation of Hydrocarbons. Shown in the equation as Alkyl and R_R...the up arrows indicating a gas. It might simply be the choice of solvents like Red said.

But that doesn't explain why 2 packs operating under similar circumstances will have 1 pack swell and the other one remain solid. It may be slight differences in chemical purity. I've had 3 Brand M packs swell after flying for the last 6 months. After cooling the gases condense and the pack again is hard. Similar ones from a different manufacturer haven't swelled yet. ?????
Jan 16, 2010, 07:44 PM
Arc, spark and smoke...
desmobob's Avatar
Quote:
Originally Posted by Red Scholefield
What impact does it have on the performance - I haven't noticed much in that regard. Swollen packs still giving good performance after 3 years use.

I have four old Apex brand 3S 2100mah packs that have seen limited use and careful, balanced charging. I didn't use them at all last year. I just opened the ammo can they're in and was a little sad to see their condition. One is pretty swollen and one is just a tiny bit thicker than the other two, which appear to be as new.

From reading this thread, it would seem that it is not a horrible risk to charge and use swollen packs. I was going to toss two of these batteries.....


Comments?

Good flying,
desmobob
Jan 16, 2010, 09:28 PM
Registered User
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Last edited by dfrazier; Jan 16, 2010 at 10:14 PM.
Jan 16, 2010, 09:36 PM
Boffin
rpage53's Avatar
Kokam (back in the day) said it was mainly carbon dioxide but this wouldn't decompose and allow the swelling to subside -- unless the pack was leaking. The electrolyte could vaporize from overheating (the hydrocarbons in Hoppy's reference) and then condense again.

Rick.
Jan 16, 2010, 10:14 PM
Boffin
rpage53's Avatar
This paper:
Calendar life study of Li-ion pouch cells
Qi Zhanga and Ralph E. White
Journal of Power Sources
Volume 173, Issue 2, 15 November 2007, Pages 990-997
http://www.sciencedirect.com/science...2f364430ed23de

says that at low temperatures degradation is usually due to changes in the Li electrode but that at higher temperatures, the carbon anode degenerates and produces CO2. "The claim is also supported by the observation that the surfaces of used carbon electrodes stored at high temperatures were entirely covered by white products which are highly reactive with air to release gas."

They also demonstrated the loss in capacity and increase in impedance with storage at high temperatures.

Rick.
Jan 16, 2010, 10:52 PM
Space Coast USA
hoppy's Avatar
Quote:
Originally Posted by desmobob

From reading this thread, it would seem that it is not a horrible risk to charge and use swollen packs. I was going to toss two of these batteries.....


Comments?

Good flying,
desmobob
IMO, that is not a good assumption. Charging packs that are swollen has resulted in many a fire. I think we, at least I am, are talking about packs that puff a little during use and return to normal size upon cooling, not packs that are swollen and stay swollen.

If yours are permanently puffed, I'd toss them after discharging.
Jan 16, 2010, 11:04 PM
Space Coast USA
hoppy's Avatar
Quote:
Originally Posted by rpage53
This paper:
Calendar life study of Li-ion pouch cells
Qi Zhanga and Ralph E. White
Journal of Power Sources
Volume 173, Issue 2, 15 November 2007, Pages 990-997
http://www.sciencedirect.com/science...2f364430ed23de

says that at low temperatures degradation is usually due to changes in the Li electrode but that at higher temperatures, the carbon anode degenerates and produces CO2. "The claim is also supported by the observation that the surfaces of used carbon electrodes stored at high temperatures were entirely covered by white products which are highly reactive with air to release gas."

They also demonstrated the loss in capacity and increase in impedance with storage at high temperatures.

Rick.
.

Interesting to me is that 59F is about as good as 41F for storage and that 95F is quite bad in comparison.
Jan 16, 2010, 11:22 PM
Arc, spark and smoke...
desmobob's Avatar
Quote:
Originally Posted by hoppy
IMO, that is not a good assumption. Charging packs that are swollen has resulted in many a fire. I think we, at least I am, are talking about packs that puff a little during use and return to normal size upon cooling, not packs that are swollen and stay swollen.

If yours are permanently puffed, I'd toss them after discharging.

Ah ha....

Two of mine ARE permanently puffed, and I think the reason is that at least one of them was put away fully charged. (Although I've read the yellow Apec batteries had a reputation for puffing easily.)

My new iCharger 106B+ has a "storage charge" feature to bring the batteries down to the right voltage for storage. That should help my LiPo survival rate in the future. I have two new EonX batteries and will be buying a few of the newest Thunder Power offerings, too.

Good flying (and safe charging),
desmobob
Jan 16, 2010, 11:34 PM
I will be an angry old man!
marc1's Avatar
Quote:
Originally Posted by desmobob

My new iCharger 106B+ has a "storage charge" feature to bring the batteries down to the right voltage for storage.
"Storage charge", as the name implies, won't "bring the batteries down", it will charge them up to 3.85V. Useful after a flight. You can use the discharge feature to bring them down to 3.85V, but you will need to set about 3.70 (under load) to get 3.85V at rest (depending on the pack size and if you are just using the internal discharger or an external load as well).


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