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Your thoughts on flat batteries
#1
Hi!

I am new here, but I have been reading for a long time.

Recently I see more and more people complaining about issue, that 18650 from laptops are harder and harder to get. What do you think about flat batteries? I have a bunch of reclaimed flat batteries from laptop packs, some are lithium-polymer pouch but I think that most are lithium-ion metal-case cells.
 
Personally, whey it is harder to get 18650 I believe that flat cells are good alternative. They have safety features like vent holes and very conveniently most have integrated, resealable theremo-fuse that opens when you pull too much current and fuse heats. 

Two things that I do not like - metal cases are positive instead of negative like 18650 cell shell, and it is almost impossible get datasheets for them.

Photo: one Samsung SDI cell from a loot of ~30. Tested a few, some worn out with ~1800-2100 mAh, some good ~3500 mAh. Didn't find datasheet, so I do not know what nominal capacity is. 

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#2
These are called Pouch or LiPo cells (not all pouch cells are LiPo, though. LiPo = Lithium Polymer)
Proceed with caution. Knowledge is Power! Literally! Cool 
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#3
that one looks bulged.
the ones i have are flat.
and yes if you have a bunch they can be used as easily as cylindrical cells.
some applications they are better at.
like converting led worklights.
a lot of these in laptop packs and esp phones are 4.35v.
treating them as 4.2v extends their life.
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#4
For reference the soft foil sided cells are called pouch (polymer) cells and the hard cased cells are referred to as prismatic cells. Having the positive electrode as the exterior of the case shouldn't make a difference. The swelling of the pouch cells are more of an issue to deal with which is why I've been working with prismatics so far. There really aren't that many different types of cell sizes when working with cells above 2,0000 mah which is what I like to use. There is finally getting to be information out there. Here's Samsung's page -

https://www.samsungsdi.com/lithium-ion-b...phone.html

18650s are going away. Pouch cells are much cheaper to produce and seem to be the future.
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#5
Pros:
- useful for smart-phone bricks (as external batteries)
- useful for various other devices that need to be very flat (like some lite notebooks)
- usually higher life-cycle

Cons:
- way easier to damage
- less specific energy
- less energy density
- more unstable and more prone to defects
- less max current provided vs the same amount of electrolyte under cylinder form
- more thermal damage when in thermal runaway
- higher cost
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#6
(09-16-2020, 11:42 AM)Overmind Wrote: - less specific energy
- less energy density

That is not a big issue when you are building stationary powerwall, unless you want to cover whole house with it and go for the most kWh rather than some amount like 20 kWh.
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#7
Pouch cells seems like a pain in the ass. It's only starting to get traction because of the disposable ways with everyone is going with ultra thin. You can thank apple et all for that. There's no more swapping out of old batteries, just throw the laptop away after 3 years. The shape isn't standard, so there's no way to figure out how to best mount it or even just to weld the tabs. It's another one of those do first and think later about the consequences.

At least the 18650 it's possible to strip and reuse.

This is not saying all pouch cells are bad. Look at a nissan leaf cell, it's ultimately a pouch cell but with terminals that make it usable. It's also encased so it's somewhat protected and somewhat compressed (even though you do need to compress it further when installed). Oh yeah, that's another downside, pouch cells do need to have a structure since it can expand during use.

No after the 18650 dries out it's most likely looking at EV cells.
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#8
(09-17-2020, 05:06 PM)cichy45 Wrote:
(09-16-2020, 11:42 AM)Overmind Wrote: - less specific energy
- less energy density

That is not a big issue when you are building stationary powerwall, unless you want to cover whole house with it and go for the most kWh rather than some amount like 20 kWh.

If building a stationary powerwall using small cells presents its own challenges, I finding large format batteries like prismatic or modules to be the ideal route for anything at scale.  One way or another, you pay for it.

Most of my 18650 and pouch cells are used in smaller projects and portables.
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#9
(09-17-2020, 05:06 PM)cichy45 Wrote:
(09-16-2020, 11:42 AM)Overmind Wrote: - less specific energy
- less energy density

That is not a big issue when you are building stationary powerwall, unless you want to cover whole house with it and go for the most kWh rather than some amount like 20 kWh.

Stationary = LiFePo4. Since you have the storage space, you can focus more on safety and life-cycles.
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#10
(09-18-2020, 12:32 PM)Overmind Wrote: Stationary = LiFePo4. Since you have the storage space, you can focus more on safety and life-cycles.

If you can sorce them - yes. However most people seems to have easier acces to Li-Ion rather than LiFePO4.
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